Determination of cobalt and zinc in highpurity niobium, tantalum, molybdenum and tungsten metals by atomicabsorption spectrophotometry after separation by extraction

A method for determining 0.0005-0.05% of cobalt and zinc in high-purity niobium, tantalum, molybdenum and tungsten metals by atomic-absorption spectrophotometry is described. After sample dissolution, cobalt and zinc are separated simultaneously from the matrix materials by chloroform extraction of their thiocyanatediantipyrylmethane ion-association complexes, at pH 3.25, from a citric acid medium approximately 1.2M in sodium thiocyanate. Interference from copper is eliminated with thiourea. Large amounts of iron interfere under the recommended conditions, but moderate amounts may be present in the sample solution without causing appreciable error in the results. Phosphorus (as orthophosphate) interferes in the extraction of cobalt from tungsten solutions. Moderate amounts of other impurities do not interfere in the proposed method.     

Determination of vanadium in refractory metals, steel, cast iron, alloys and silicates by extraction of an NBPHA complex from a sulphuric-hydrofluoric acid medium

A method for determining up to 0.15% of vanadium in high-purity niobium and tantalum metals, cast iron, steel, non-ferrous alloys and silicates is described. The proposed method is based on the extraction of a red vanadium(V)-N-benzoyl-N-phenylhydroxylamine complex into chloroform from a sulphuric-hydrofluoric acid medium containing excess of ammonium persulphate as oxidant. The molar absorptivity of the complex is 428 l.mole(-1).mm(-5) at 475 nm, the wavelength of maximum absorption. Interference from chromium(VI) and cerium(IV) is eliminated by reduction with iron(II). Common ions, including large amounts of titanium, zirconium, molybdenum and tungsten, do not interfere.     

Extractions with long-chain amines-III: colorimetric determination of molybdenum as thioglycollate

A highly selective and sensitive colorimetric determination of molybdenum(VI) based on its extraction with a chloroform solution of trioctylamine from solutions of acetic and thioglycollic acid (TGA) is described. The yellow chloroform extract containing the molybdenum-TGA complex is measured at 370 nm. With a single extraction it is possible to determine small amounts of molybdenum in the presence of very large concentrations of almost all metals. Only bismuth, mercury and tungsten interfere.     

Analytical separation of rhenium by extraction with n-benzylaniline in chloroform from sulphuric acid media

Analytical separation of rhenium(VII) is achieved by solvent extraction with N-benzylaniline in chloroform from sulphuric acid media. Few cations interfere: common anions such as phosphate, tartrate, citrate, oxalate, fluoride, EDTA and ascorbic acid do not interfere. A simple method is described for the separation of micro amounts of rhenium from macro amounts of molybdenum, tungsten, niobium and tantalum. The method also separates rhenium from V, Cr, Se, Te, Os, Ru, Rh, Pd and Pt. The molar absorptivity of rhenium thiocyanate complex in butyl acetate and diisopropyl ether is 40280 ± 280 at 430 nm.     

Determination of aluminium in molybdenum and tungsten metals, iron, steel and ferrous and non-ferrous alloys with pyrocatechol violet

A method for determining 0.001-0.10% of aluminium in molybdenum and tungsten metals is described. After sample dissolution, aluminium is separated from the matrix materials by chloroform extraction of its acetylacetone complex, at pH 6.5, from an ammonium acetate-hydrogen peroxide medium, then back-extracted into 12M hydrochloric add. Following separation of most co-extracted elements, except for beryllium and small amounts of chroinium(III) and copper(II), by a combined ammonium pyrrolidincdithiocarbamate-cupfen-on-chlorofonn extraction, aluminium is determined spectrophotometrically with Pyrocatechol Violet at 578 nm. Chromium interferes during colour development but beryllium, in amounts equivalent to the aluminium concentration, does not cause significant error in the results. Interference from copper(II) is eliminated by reduction with ascorbic acid. The proposed method is also applicable to iron, steel, ferrovanadium, and copper-base alloys after preliminary removal of the matrix elements by a mercury cathode separation.     

Determination of manganese in high-purity niobium, tantalum, molybdenum and tungsten metals with pan

A spectrophotometric method for the determination of 0.0005-0.10% of manganese in high-purity niobium, tantalum, molybdenum and tungsten metals is described. The matrix materials are separated from the manganese by extraction as cupferrates, after sample dissolution, then the red complex formed between manganese(II) and 1-(2-pyridylazo)-2-naphthol, PAN, is extracted into chloroform from an ammoniacal tartrate-cyanide medium. The absorbance of the extract is determined at 562 mmicro. With the exception of zinc and lead, other impurities present in the four high-purity metals described do not interfere with the proposed method.     

Separation of tungsten from molybdenum by liquid-liquid extraction and extraction chromatography using thiocyanate and a quaternary ammonium salt

Methods were developed for the separation of tungsten from molybdenum by liquid-liquid extraction and extraction chromatography using thiocyanate and a quaternary ammonium salt, Zephiramine. Tungsten was extracted into chloroform as an ion associate of tungsten(V)-thiocyanate complex and Zephiramine cation was retained on a column of Teflon powder coated with Zephiramine, but molybdenum(III) was neither extracted nor retained. The extraction chromatographic method was successfully applied to the determination of trace amounts of tungsten in molybdenum by neutron activation analysis.     

Improved tribenzylamine-silver bromide extraction/atomic-absorption spectrophotometric method for the determination of silver in ores, related materials and zinc process solutions

An improved tribenzylamine extraction/atomic-absorption method for the determination of silver in ores, related materials and zinc process solutions is described. The method, which involves the separation of silver by a single methyl isobutyl ketone extraction of the tribenzylamine-silver bromide ion-association complex from ~ 0.5-2M sulphuric acid-0.14M potassium bromide, is simpler and more rapid than a previous method based on a triple chloroform extraction of the complex. Silver is stripped with 12M hydrochloric acid containing 1% thiourea as a complexing agent. Thiourea is destroyed with nitric and perchloric acids and silver is ultimately determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 328.1 nm, in a 10% v v hydrochloric acid-1% v v diethylenetriamine medium. Cadmium and bismuth are partly co-extracted but do not interfere. Results obtained by this method are compared with those obtained previously by the tribenzylamine/chloroform extraction method and with those obtained by a direct acid-decomposition/atomic-absorption method.     

Extractive separation and spectrophotometric determination of tungsten as ferrocyanide

Tungsten, in amounts ranging from micrograms to milligrams, can be extracted into isoamyl alcohol, as the tungsten(V) ferrocyanide complex obtained by reduction of tungsten(VI) with tin(II) in 4M hydrochloric acid containing ferrocyanide. It can thus be separated from iron, cobalt, chromium, manganese, arsenic, antimony, bismuth, silicon, calcium and copper, their precipitation being prevented by addition of glycerol and, in the case of iron, sulphosalicyclic acid. Molybdenum, vanadium and nickel are not separated from tungsten, however. Tungsten can also be determined spectrophotometrically as tungsten(V) ferrocyanide. The absorbance of the brown complex is measured in aqueous solution or preferably after extraction into isoamyl alcohol. As many alloying elements interfere, they should be separated by the ferrocyanide extraction or other suitable method. Both the separation and the determination methods give satisfactory results with an overall error of not more than 0.5% in the analysis of practical samples containing low or high percentages of tungsten.     

Spectrophotometric determination of boron in iron and steel with curcumin after separation by 2-ethyl-1,3-hexanediol-chloroform extraction

A simple and reliable method for determining approximately 0.0001% or more of total boron in iron and low- and high-alloy steels is described. After the sample is decomposed at <70 degrees in the presence of hydrogen peroxide and potassium hydrogen fluoride, the insoluble material is filtered off and ultimately fused with sodium carbonate. The cooled melt is dissolved in dilute hydrochloric acid and the solution is combined with the main solution. Fluoride is subsequently complexed with zirconium and boron is separated from iron and other elements by extraction as borate from 1M sulphuric acid medium into chloroform containing 2-ethyl-1,3-hexanediol. Boron, in a 1-ml portion of the extract, is ultimately determined spectrophotometrically at 550 nm in an ethanol medium, after formation of the curcumin rosocyanin complex in a glacial acetic acid-concentrated sulphuric acid medium. Acid-soluble and acid-insoluble boron can also be determined. Common ions, including large amounts of manganese, chromium, vanadium, titanium, molybdenum, tungsten, niobium and tantalum do not interfere.     

Determination of titanium in high-purity molybdenum and tungsten metals with diantipyrylmethane after separation by extraction of its cupferron complex

A method for determining 0.0005–0.10% of titanium in high-purity molybdenum and tungsten metals is described. After sample dissolution, titanium is separated from the matrix materials by chloroform extraction of its cupferronate from an alkaline (pH 8) tartrate-EDTA medium, then determined spectrophotometrically with diantipyrylmethane at 390 nm. Interference from manganese during extraction is eliminated with sodium sulphite. Iron, zirconium, thorium, tin, aluminium and antimony are partially extracted under the proposed conditions, but moderate amounts of these elements may be present in the sample solution without causing error in the results. Interference from iron(III) during colour development is eliminated with ascorbic acid. Other impurities in the two high-purity metals described do not interfere in the proposed method.     

Extractive separation of molybdenum as Mo(V) xanthate from Iron, vanadium, Tungsten, copper, uranium and other elements

A simple and selective extraction of molybdenum is described. Tungsten is masked with tartaric acid and molybdenum(VI) is reduced in 2M hydrochloric acid by boiling with hydrazine sulphate. Iron, copper and vanadium are then masked with ascorbic acid, thiourea and potassium hydrogen fluoride respectively. The molybdenum(V) is extracted as its xanthate complex into chloroform, from 1M hydrochloric acid that is 0.4M potassium ethyl xanthate. The complex is decomposed by excess of liquid bromine, and the molybdenum is stripped into alkaline hydrogen peroxide solution. The molybdenum is then determined by standard methods. Large amounts of Cu(II), Mn(II), Fe(III), Ti(IV), Zr, Ce(IV), V(V), Nb, Cr(VI), W(VI), U(VI), Re(VII) and Os(VIII) do not interfere. Several synthetic samples and ferromolybdenum have been rapidly and satisfactorily analysed by the method.     

Determination of molybdenum in ores, iron and steel by atomic-absorption spectrophotometry after separation by alpha-benzoinoxime extraction or further xanthate extraction

A simple and moderately rapid method for determining 0.001% or more of molybdenum in ores, iron and steel is described. After sample decomposition, molybdenum is separated from the matrix elements, except tungsten, by chloroform extraction of its alpha-benzoinoxime complex from a 1.75 M hydrochloric-0.13 M tartaric acid medium. Depending on the amount of tungsten present, molybdenum, if necessary, is back-extracted into concentrated ammonia solution and subsequently separated from coextracted tungsten by chloroform extraction of its xanthate complex from a 1.5M hydrochloric-0.13M tartaric acid medium. It is ultimately determined by atomic-absorption spectrophotometry, at 313.3 nm, in a 15% v/v hydrochloric acid medium containing 1,000 microg/ml of aluminium as the chloride, after evaporation of either extract to dryness with nitric, perchloric and sulphuric acids and dissolution of the salts in dilute ammonia solution.     

Spectrophotometric determination of tantalum in ores and mill products with brilliant green after separation by methyl isobutyl ketone extraction of tantalum fluoride

A method for determining ~ 0.001% or more of tantalum in ores and mill products is described. After fusion of the sample with sodium carbonate, the cooled melt is dissolved in dilute sulphuric-hydrofluoric acid mixture and tantalum is separated from niobium and other matrix elements by methyl isobutyl ketone extraction of its fluoride from 1M hydrofluoric acid-0.5M sulphuric acid. The extract is washed with a hydrofluoric-sulphuric acid solution of the same composition to remove co-extracted niobium, and tantalum is stripped with dilute hydrogen peroxide. This solution is acidified with sulphuric and hydrofluoric acids and evaporated to dryness, and the residue is dissolved in oxalic-hydrofluoric acid solution. Tantalum is ultimately determined spectrophotometrically after extraction of the blue hexafluorotantalate-Brilliant Green ion-association complex into benzene from a 0.05M sulphuric acid-0.5M hydrofluoric acid-0.2M oxalic acid medium. The apparent molar absorptivity of the complex is 1.19 x 10(4) l.mole(-1).mm(-1) at 640 nm, the wavelength of maximum absorption. Common ions, including iron, aluminium, manganese, zirconium, titanium, molybdenum, tungsten, vanadium, tin, arsenic and antimony, do not interfere. Results obtained by this method are compared with those obtained by an X-ray fluorescence method.     

Ultraviolet spectrophotometric determination of tungsten(VI) with ammonium 1-pyrrolidinecarbodithioate

A simple and rapid ultraviolet spectrophotometric method is proposed for the determination of trace amounts of tungsten(VI) with ammonium 1-pyrrolidinecarbodithioate (APDC). The method is based on measurement of the absorbance of the tungsten APDC complex in fairly concentrated hydrochloric acid medium; no extraction is required. The complex is formed at an initial acidity of 6M hydrochloric acid and has an absorption maximum at 250 nm. The high absorption of the reagent blank at 250 nm disappears on decomposition of excess of reagent by heating. Beer's law is obeyed over the range 0.43–3.2 ppm of tungsten(VI). The molar absorptivity of the complex is 4.5 × 10⁴ l.mole⁻¹ .cm⁻¹ at 250 nm. Tenfold amounts of aluminium, magnesium, calcium, cobalt, iron(II), lead, silver, sodium and titanium do not interfere in the determination of 50 μg of tungsten (VI).     

Spectrophotometric determination of arsenic in concentrates and copper-base alloys by the molybdenum blue method after separations by iron collection and xanthate extraction

A method for determining 0.0001-1% of arsenic in copper, nickel, molybdenum, lead and zinc concentrates is described. After sample decomposition, arsenic is separated from most of the matrix elements by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Following reprecipitation of arsenic and iron, the precipitate is dissolved in approximately 2 M hydrochloric acid and the solution is evaporated to a small volume to remove water. Arsenic(V) is reduced to the tervalent state with iron(II) and separated from iron, lead and other co-precipitated elements by chloroform extraction of its xanthate from an 11M hydrochloric acid medium. After oxidation of arsenic(III) in the extract to arsenic(V) with bromine-carbon tetrachloride solution, it is back-extracted into water and determined by the molybdenum blue method. Small amounts of iron, copper and molybdenum, which are co-extracted as xanthates, and antimony, which is co-extracted to a slight extent as the chloro-complex under the proposed conditions, do not interfere. The proposed method is also applicable to copper-base alloys.     

Extraction—spectrophotometric determination of palladium(ii) with 2-nitroso-5-diethylaminophenol

An extraction—spectrophotometric determination of palladium(II) with 2-nitroso-5-diethylaminophenol is described. Complex formation and extraction of the complex with chloroform are possible with aqueous phases of about 2.5 M sulfuric acid. The molar absorptivity of the complex is 4.38 X 10⁴ l mol^-1 cm^-1 at 486 nm. Few of the common ions interfere at concentrations of 10^-4–10^-3 M; more than 10^-5 M Ir(IV), 10^-5 M W(VI), 5 × 10^-6 M Au(III) and 10^-6 M iodide cause negative errors. The method can be applied to the determination of palladium in catalysts for automobile exhaust purifiers.     

The extraction and determination of tungsten with tetraphenylarsonium chloride

A rapid, accurate and selective spectrophotometric method for tungsten is described. Tetraphonylarsonium chloride is used to form an insoluble ion-pair tetraphenylarsonium thiocyanato-tungstate, with tungsten previously reduced with tin(II) chloride in 6 9 M HCl The ion-pair is formed the addition of thiocyanate, extracted into chloroform, and the absorbance is measured at 406 mm. The method is selective for tungsten under the conditions employed when niobium is masked with fluoride. The sensitivity is 12.58 μg W/ml of chloroform extract. The method has been applied successfully to 8 steels iand 2 heat-resisting alloys which contain widely varying amounts of tungsten and otther metals.     

Extraction-spectrophotometric determination of vanadium with N-m-tolyl-N-phenylhydroxylamine and its application to coal and coal fly-ash

N-m-Tolyl-N-phenylhydroxylamine is proposed for the spectrophotometric determination of small amounts of vanadium. The reddish-violet complex formed with the reagent in 3-6M hydrochloric acid after extraction with chloroform shows an absorption maximum at 530 nm, and obeys Beer's law for 0-76.5 mug of vanadium in 10 ml of chloroform. The proposed method has been successfully applied to the determination of vanadium in coal and coal fly-ash.     

Spectrophotometric determination of tungsten with thiocyanate

The yellow W(V) thiocyanate complex is formed by shaking sodium tungstate solution in 0.2-0.8M potassium thiocyanate and 4-5M hydrochloric acid, with mercury. It is extracted with 2% tribenzylamine solution in chloroform and measured at 410 nm. U, Ti, V, Cr, Fe, Co, Ni, Mn, Al, Pb, Sn, Bi, Pd, Sb and Cu do not interfere. Pt and Mo in amount equal to that of tungsten give errors of up to 0.4 and 2% respectively. The sensitivity is 0.013 mug ml and Beer's law is obeyed up to 24 mug ml .