Extraction of uranium with 2,3-dihydroxynaphthalene and cetyltrimethylammonium bromide, and its fluorimetric determination in silicate rocks

A novel procedure for the extraction of uranium has been described. UO₂ ²⁺ forms a 1:3 anionic complex with 2,3-dihydroxynaphthalene in the pH range, 4–12. This anionic complex is best extracted into ethyl acetate at pH 11–12 under the influence of a counter cation, cetyltrimethylammonium bromide. This extraction technique has been extended to the separation of uranium from silicate rock matrices for its determination by fluorimetry. Except Co, Cr, and Fe, most elements present in silicate rocks do not interfere. While the interferences of Co and Cr are suppressed by the addition of EDTA, iron is removed by prior extraction at pH 4–5 as its neutral complex with 2,3-dihydroxynaphthalene. The results compare favourably with those obtained from the conventional technique, i.e., extraction of uranium in ethyl acetate from NHO₃ medium under the influence of Al(NO₃)₃ ^.9H₂O as salting out agent. The extraction system under study is capable of separating even ultra-trace amounts of uranium quantitatively from complex matrices of rock samples. Besides, the method is simple, rapid, cost effective and precludes the use of reagents like nitric acid and aluminum nitrate (salting out agent) required in bulk quantities in the conventional system.     

Photometric determination of phosphorus in silicate rocks

Phosphorus in silicate rocks may bedeterminedaccurately by the photometric molybdovanadophosphoric acid method following decomposition of the sample with nitric-hydrofluoric acid.     

Photometric determination of arsenic in silicate rocks

Summary The method described consists in decomposing the silicate rock sample by fusion with sodium hydroxide or sodium hydroxide-peroxide, leaching the melt with water, evolving arsine from the filtrate, and finally determining arsenic by photometric evaluation of molybdenum blue. Satisfactory accuracy has been demonstrated for the range 0.0 to 20 p. p. m. As, for which the method is particularly intended.

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Zusammenfassung Zur Bestimmung des Arsengehaltes in Silikatgesteinen wird die Probe durch Schmelzen mit Natriumhydroxyd und gegebenenfalls Natriumperoxyd aufgeschlossen. Aus dem Filtrat der wäßrigen Lösung dieser Schmelze wird Arsenwasserstoff entwickelt und in natriumhydrogenkarbonathältiger Jodlösung aufgefangen. Das hierbei entstehende Arsenat wird nach Zugabe von Molybdatreagens und Bisulfit photometrisch bestimmt. Für Arsengehalte unter 0,02% werden nach dieser Methode Resultate von zufriedenstellender Genauigkeit erhalten.

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Résumé La méthode décrite consiste en la décomposition de l'échantillon de roche silicatée par fusion avec la soude ou le peroxyde de sodium, reprenant la partie fondue par l'eau, libérant l'hydrogène arsénié du filtrat et finalement dosant l'arsenic par colorimétrie du bleu de molybdène. Une précision suffisante a été mise en évidence dans le domaine de 0,0 à 20 p. p. m. d'arsenic pour lequel la méthode convient particulièrement bien.

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Fulbright Scholar.     

Determination of trace quantities of scandium in silicate rocks by a combined ion exchange-spectrophotometric method

A spectrophotometric determination of scandium in silicate rocks has been developed with arsenazo as the color reagent. After the decomposition of samples with a hydrofluoric-perchloric acid mixture, traces of scandium are separated from interferences by cation- and anion-exchange in acid sulfate media and anion exchange in hydrochloric acid solution. The successive 3 steps, with an intermediate concentration step, yield scandium in a sufficiently pure state for spectrophotometric determination.     

Rapid determination of nanogram amounts of tellurium in silicate rocks

A hydride-generation flameless atomic-absorption technique is used to determine as little as 5 ng g^-1 tellurium in 0.25 g of silicate rock. After acid decomposition of the sample, tellurium hydride is generated with sodium borohydride and the vapor passed directly to a resistance-heated quartz cell mounted in an atomic-absorption spectrophotometer. Analyses of 11 U.S. Geological Survey standard rocks are presented.     

The titrimetric determination of calcium and magnesium in silicate rocks

A cation-exchange scheme is described for the separation of calcium and magnesium from interfering elements in rapid silicate analysis. Interfering elements can be eluted from the ammonium form of Zeo-Karb 225 with a solution of the ammonium salt of ethylenediaminetetraacetic acid at pH 4.5. Calcium and magnesium are not eluted with this reagent but can be eluted consecutively with ammonium chloride solution and titrated photometrically with EDTA. Calcium and magnesium can be separated quantitatively from Al, Fe, Ti, Mn, Bi, Cd, Cr, Co, Cu, Pb, Mo, Ni, U, V, rare earths, and Zn.     

Anion-exchange separation and spectrophotometric determination of vanadium in silicate rocks

A combined anion-exchange-spectrophotometric method has been developed for the determination of vanadium in silicate rocks. A rock sample weighing about 0.1 g is decomposed with a mixture of sulphuric and hydrofluoric acids and after removal of HF the residue is taken up with dilute sulphuric acid. This solution is adjusted to be 0.05M in sulphuric acid and contain 0.3% hydrogen peroxide, and is passed through a column of Amberlite CG 400 (sulphate form). The sorbed vanadium is eluted with 30 ml of 1M hydrochloric acid. The effluent is evaporated to dryness, made 0.1M in hydrochloric acid and 3% in hydrogen peroxide content, and passed through a column of Amberlite CG 400 (chloride form) to get rid of accompanying thorium and zirconium. Vanadium is stripped by elution with 20 ml of 1M hydrochloric acid and subsequently determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. The detection limit is 0.4 ppm.     

Multi-element determination in silicate rocks by instrumental neutron activation analysis

Instrumental neutron activation analysis technique was applied for the determination of 20 elements in 54 silicate rock samples which belong to three sedimentary geological formations located in the western desert of Iraq. The samples along with USGS standards were irradiated in an IRT-5000 reactor at a neutron flux of 3.7·10¹³ n·cm^–2·s^–1 The following minor and trace element constituents have been determined: Na, K, Ca, Fe, Sc, Cr, Co, Zr, Ce, La, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th and U.     

Anion-exchange separation and spectrophotometric determination of molybdenum and tungsten in silicate rocks

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum and tungsten in silicate rocks. After the decomposition of samples with a mixture of sulphuric, nitric and hydrofluoric acids, traces of molybdenum and tungsten are separated from other elements by anion-exchange in acid sulphate media containing hydrogen peroxide. The adsorbed molybdenum and tungsten can easily be stripped from the column by elution with sodium hydroxide-sodium chloride solution. The adsorption and desorption steps provide selective concentration of molybdenum and tungsten, allowing the simultaneous spectrophotometric determination of the two metals with dithiol. Results on the quantitative determination of molybdenum and tungsten in the U.S. Geological Survey standard samples are included.     

Micelle mediated extraction of titanium and its ultra-trace determination in silicate rocks

A highly sensitive method for extractive spectrophotometric determination of titanium in silicate rocks is described. Titanium in the range 0-10 microg as TiO2 is extracted into benzene or toluene by the formation of a ternary complex of the metal with thiocyanate (SCN-) and cetyltrimethylammonium bromide (CTA) in the ratio 1:2:2. A deep yellowish-orange ternary complex thus formed is suitable for the determination of titanium at wavelength 421 nm. The optimum colour intensity of this ternary complex was attained when the complex was extracted from an aqueous solution having concentrations of thiocyanate and HCl, in the range, 1.5-2.5 and 1-5 mol L(-1), respectively. The molar absorptivity and Sandell's sensitivity of the extracted species were found to be 1.1-1.0x10(5) L mol(-1) cm(-1) and 0.47 ng cm(-2) (referred to titanium), respectively, at lambda(max) of 421 nm. Except Fe3+, Nb5+ and V5+, no interference was encountered in the estimation of titanium. While up to 10 mg L(-1) Nb and V did not interfere in the determination of titanium, the interference of Fe(3+) was eliminated by reducing it to Fe2+ using SnCl2 solution. The method is highly sensitive and selective. The results obtained for titanium estimation in a host of silicate rock samples have been found to be highly reproducible, accurate and favourably comparable with certified values of reference materials and those obtained from standard methods.     

Non-aqueous cerimetric determination of phenylhydrazides

A non-aqueous oxidimetric method is described for the determination of some carboxylic acid phenylhydrazides with ammonium hexanitratocerate(IV) in acetonitrile. The end-points have been detected visually with chemical indicators (diphenylamine, diphenylbenzidine, Methyl Red, Malachite Green, Janus Green, Gentian Violet) and potentiometrically. The compounds are smoothly, rapidly and quantitatively oxidized with a two-electron change per hydrazino group. The method is simple, accurate, reliable and widely applicable.     

Determination of scandium and lanthanum in silicate rocks and coal with a simplified separation procedure and atomic absorption spectrometry

Simplified procedures for the quantitative separation and enrichment of scandium and lanthanum in igneous rocks are described. Co-precipitation with calcium oxalate is followed by co-precipitation with hydrated iron(III) oxide. Electrothermal and flame atomic absorption spectrometry are applied. The procedures are verified with synthetic sample solutions and the eighteen international reference samples of rocks and coal compare favourably with previously reported data and with data obtained by emission spectrography.     

Non-aqueous cerimetric determination of thioureas

Ammonium hexanitratocerate (in acetonitrile) solution has been used as an oxidimetric reagent for the visual and potentiometric determination of thiourea and its alkyl derivatives in acetonitrile medium. The thioureas are oxidized to their corresponding disulphides. The method is simple, accurate, reliable and widely applicable.     

A standard addition titration method for the determination of fluorine in silicate rocks

Silicate minerals have been analysed for fluoride, after decomposition with sodium carbonate and zinc oxide, by a standard addition titration technique. The main advantages of the method are its precision and the elimination of errors arising from separate preliminary calibration.     

Non-aqueous determination of inorganic salts

The procedures suggested for the determination of salts in nonaqueous solutions have been limited almost wholly to the analysis of amine salts and salts of the alkali and alkaline earth metals. Other salts are usually assayed by a variety of specific cationic or anionic procedures. By the proposed method, salts of all types can be determined titrimetrically so long as the compound will participate in an anion-exchange reaction. The procedure simply involves acidification of the salt with an excess of a strong acid, addition of a nonaqueous solvent and a differentiating potentiometric titration. Carbonate and hydroxide impurities do not interfere in the analysis and the solubility difficulties experienced in other nonaqueous procedures are not encountered in this method.     

A selective lon-exchange separation and spectrophotometric determination of traces of copper in silicate rocks

Summary A combined cation-exchange separation-spectrophotometric procedure has been worked out for the accurate determination of traces of copper in silicate rocks. Silicates are opened up with sulfuric and hydrofluoric acids. The residue is taken up into a 0.5 M hydrochloric acid −0.05 M oxalic acid −1% hydrogen peroxide solution and loaded on a strongly acidic cation-exchange resin column. Polyvalent ions including ferric ions do not adsorb on the column, while copper (II) retains together with divalent metal ions as well as aluminum (III). Copper (II) can selectively be eluted by a small volume of 0.05 M thiosulfate solution. This fraction is sufficiently pure to allow a direct spectrophotometric determination of copper with Na-DDTC without the addition of tartrate and EDTA as masking agents. Quantitative results are quoted for the determination of copper in international standard rocks of the Geological Survey of Japan (GSJ) and the U.S. Geological Survey (USGS).     

Electrothermal atomisation for atomic-absorption determination of some rare earths in silicate rocks and minerals

Summary The interfering effects due to the composition of the silicate matrix of a common geological sample have been overcome by an ion-exchange separation procedure.The early described cation-exchange device allows a complete separation of the rare earth element group (plus barium, yttrium and scandium) from the major and minor elements of the matrix (i. e. calcium, iron, aluminium, sodium, etc.).Some analytical flameless atomic absorption procedures have been carried out on the eluate fraction: dysprosium, holmium, thulium, ytterbium and europium are determined in international standard rocks and minerals. The REE (rare earth elements) values fall well into the range reported in literature.

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Elektrothermische Zerstäubung einiger Seltener Erden in Silikatgesteinen und Mineralen zum Zweck ihrer Bestimmung durch AAS

Zusammenfassung Die auf die Zusammensetzung von Silikaten zurückzuführenden Störungen bei der Analyse gewöhnlicher geologischer Proben lassen sich durch Ionenaustausch beseitigen. Der früher beschriebene Kationenaustausch ermöglicht die vollständige Abtrennung der Seltenen Erden (mit Barium, Yttrium und Scandium) von den Haupt- und Nebenbestandteilen der Matrix (d. h. Calcium, Eisen, Aluminium, Natrium usw.). Einige Verfahren zur analytischen AAS des Eluats wurden ausgearbeitet. Dysprosium, Holmium, Thulium, Ytterbium und Europium wurden in internationalen Standard-Gesteinsproben bestimmt. Die Ergebnisse liegen gut im Bereich der Literaturangaben.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.

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This work was carried out with a financial contribution of the Consiglio Nazionale delle Ricerche of Italy.     

Non-aqueous spectrophotometric determination of citric acid

A non-aqueous spectrophotometric method is described for the determination of citric acid in the presence of carboxylic acids and lactic acid. The method was developed as a result of critical evaluation of the Furth-Herrmann color reaction in a non-aqueous pyridine-acetic anhydride solution. The optimum conditions are described. The absorbance is read at 389 ± 2 mμ. The minimum concentration of citric acid that can accurately be determined is about 2 μg per sample.