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.     

Microanalytical determination of tin in organotin compounds

Existing procedures for the determination of tin in organotin compounds are reviewed, and a new procedure is described which can be used for the rapid microanalysis of most organotin compounds. Wet oxidation with sulphuric acid and 30% hydrogen peroxide is followed by spectrophotometric determination of the extracted ternary tin(IV)-chloride-oxine complex in chloroform. Time for a single determination is 20 min, and the relative standard deviation is 0.7% for 1-5 mg of tin. On account of their volatility, methyltin compounds must be subjected to a sealed-tube wet oxidation in sulphuric-nitric acid mixture. Addition of sulphamic acid after boiling to remove most of the nitric acid makes this compatible with the solvent extraction step. Tin present as organotin stabilizer in PVC samples can also be determined by this method, after destruction of the organic matter with sulphuric acid and 50% hydrogen peroxide.     

Pulse Polarographic: Determination of Nanogram Amounts of Ortho-Phosphate

Abstract

A procedure has been developed for the pulse polarographic determination of nanogram amounts of ortho-phosphate based on the reduction of molybdenum blue formed from 12-molydophosphate. The molybdenum blue is extracted into iso-amyl alcohol from acid solution, and the extract is then washed free of excess molybdate with dilute sulphuric acid. Finally, the molybdenum blue is back-extracted into a tartrate buffer and is pulse polarographed. Precise determinations can be made on 10 ng of PO₄ ³ ml^?11 in the polarographed solution. Determinations have been made on standard and sample ortho-phosphate solutions at the 2 ng of PO₄ ³ ml^?11 level by effecting a five-fold concentration at the extraction step.     

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.     

A new volumetric method for the determination of molybdenum(VI)

Summary A new volumetric method has been developed for the determination of molybdenum(VI). The method consists in the reduction of molybdenum(VI) by heating with a slight excess of hydrazine sulphate in 1 to 2 M hydrochloric acid medium for ten minutes on a water bath. The mixture is cooled and the molybdenum(V) obtained determined by titration with a standard solution of ceric sulphate at an overall acidity of 4 N hydrochloric acid, using diphenyl benzidine as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the mixture. Alternately the molybdenum(V) can be titrated with a standard solution of ceric sulphate at an overall acidity of 3 N hydrochloric acid using ferroin as indicator and adding 5 ml of syrupy phosphoric acid for 50 ml of the titration mixture. The molybdenum(V) can also be titrated with a standard solution of sodium vanadate in 8 N sulphuric acid medium, using N-phenyl anthranilic acid as indicator. Alternately, the titration with sodium vanadate can be made with diphenyl benzidine as indicator in 4 N acid medium, adding 5 ml of syrupy phosphoric acid and 1 ml of 1.0 M oxalic acid to catalyse the indicator action. The method now proposed is much more convenient than the methods currently available. It is simple because it does not require any costly chemicals or complicated apparatus. Furthermore, it has the advantages of great rapidity and excellent precision.     

Extraction of bivalent vanadium as its pyridine thiocyanate complex and separation from uranium, titanium, chromium and aluminium

A simple method is described for the extraction of V(II) as its pyridine thiocyanate complex. Vanadate is reduced to V(II) in 1-2N sulphuric acid by zinc amalgam. Thiocyanate and pyridine are added, the solution is adjusted to pH 5.2-5.5 and the complex extracted with chloroform. The vanadium is back-extracted with peroxide solution. Zinc from the reductant accompanies the vanadium but alkali and alkaline earth metal ions, titanium, uranium, chromium and aluminium are separated, besides those ions reduced to the elements by zinc amalgam. The method takes about 20 min and is applicable to microgram as well as milligram amounts of vanadium.     

Spectrophotometric determination of dissolved tri n-butyl phosphate in aqueous streams of Purex process

A spectrophotometric method is developed for the determination of dissolved tri-n butyl phosphate (TBP) in aqueous streams of Purex process used in nuclear fuel reprocessing. The method is based on the formation of phosphomolybdate with added ammonium molybdate followed by reduction with hydrazine sulphate in acid medium. Orthophosphate and molybdate ions combine in acidic solution to give molybdophosphoric (phosphomolybdic) acid, which upon selective reduction (with hydrazinium sulphate) produces a blue colour, due to molybdenum blue. The intensity of blue colour is proportional to the amount of phosphate. If the acidity at the time of reduction is 0.5?M in sulphuric acid and hydrazinium sulphate is the reductant, the resulting blue complex exhibits maximum absorption at 810?C840?nm. The system obeys Lambert?CBeer??s law at 830?nm in the concentration range of 0.1?C1.0???g/ml of phosphate. Molar Absorptivity was determined to be 3.1?×?10^4?L?mol^?1?cm^?1 at 830?nm. The results obtained are reproducible with standard deviation of 1?% and relative error less than 2?% and are in good agreement with those obtained by ion chromatographic technique.     

Spectrophotometric determination of molybdenum by extraction of a green molybdenum(v) species

A simple method is described for the rapid spectrophotometric determination of molybdenum in samples containing 1-60% Mo, with satisfactory accuracy. Molybdenum is reduced with excess of hydrazine sulphate in boiling 5.5M hydrochloric acid and extracted with isoamyl acetate from 7M hydrochloric acid. The green colour is measured at 720 nm against a reagent blank. Beer's law is obeyed over the range 0.08-5.4 mg of molybdenum per ml. Interference from iron and copper is removed by adding stannous chloride and thiourea respectively in slight excess. Titanium, vanadium, niobium, chromium, tungsten, nickel, uranium, and antimony do not interfere even in large amounts. Only cobalt interferes seriously.     

A fluorescence test for vanadium(V) with resorcinol

Summary In continuation of our previous work in which salicylic acid was reported to give a very sensitive and an almost specific colour reaction with vanadium(V), we have now found that vanadium(V) reacts with resorcinol in 20 N sulphuric or phosphoric acid solution to give a blue coloured product, which gives a vivid red fluorescence under filtered ultraviolet light. A sensitive test for vanadium(V) has now been developed making use of this red fluorescence or of the bright blue colour. Dichromate gives a somewhat less sensitive violet colour with the resorcinol reagent under the same conditions, but the product does not fluoresce. Manganese(VII), cerium(IV), iron(III), titanium(IV), uranium(VI), molybdenum(VI) and tungsten(VI) do not interfere with the colour reaction or the fluorescence test for vanadium(V).     

Determination of chromium in ores, rocks and related materials, iron, steel and non-ferrous alloys by atomic-absorption spectrophotometry after separation by tribenzylamine-chloroform extraction

A method for determining trace and moderate amounts of chromium in ores, concentrates, rocks, soils and clays is described. After fusion of the sample with sodium peroxide, the melt is dissolved in dilute sulphuric acid. The chromium(III) produced by the hydrogen peroxide formed is co-precipitated with hydrous ferric oxide. The precipitate is dissolved in 0.7M sulphuric acid and chromium oxidized to chromium(VI) with ceric ammonium sulphate. The chromium(VI) is extracted as an ion-association complex into chloroform containing tribenzylamine and stripped with ammoniacal hydrogen peroxide. This solution is acidified with perchloric acid and chromium determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 357.9 nm. Barium and strontium do not interfere. The procedure is also applicable to iron and steel, and nickel-copper, aluminium and zirconium alloys. Up to 5 mg of manganese and 10 mg each of molybdenum and vanadium will not interfere. In the absence of vanadium, up to 10 mg of tungsten will not interfere. In the presence of 1 mg of vanadium, up to 1 mg of tungsten will not interfere.     

The polarograph1c estimation of molybdenum in plant materials

A method has been developed whereby molybdenum is extracted from digests of plant materials by means of a-benzomoxime and chloroform from a medium of 1 % sulphuric acid solution, Following the decomposition of the extract, the molybdenum is estimated polarographically by measuring the catalytic wave in a sulphuric acid-pcrchloratc supporting electrolyte in which the sensitivity is increased tenfold over the normal wave. The method provides a selective, highly sensitive procedure, capable of determining very small quantities of molybdenum.     

Trivalent molybdenum as volumetric reducing agent

Summary The purpose of the present investigation is to introduce trivalent molybdenum as a new analytical reducing agent, in hydrochloric as well as sulphuric acid media.The solution is prepared in 9N acid by electrolytic or mercuryreduction of the hexavalent form. It is preferentially stocked and used in high acid concentrations, whereby its stability in air is optimal, falling to half its titer after nearly two months. It has been tested with success as reductant for ceric, dichromate, ferric and vanadate. It has the advantage of being used in ordinary opened burettes. Titrations were followed potentiometrically in general, and alternately visually in decinormal media, whereby molybdenum blue appears at the end-point. The percentage error in fifteen discussed experiments never surpassed ±1%. Some oxidation titrations were also undertaken using iodate and bromate, with the same degree of accuracy, provided they were conducted in 6N acid. In weaker acid concentrations, equilibria were more slowly attained, with a more or less pronounced deviation, due to some oxidisability that necessitates controlled inert atmosphere.     

铈量法快速测定镍钼矿硫酸介质加压浸出液中的钼

镍钼浸出液中的大量Fe^2＋和Fe^3＋,采用氢氧化钠沉淀分离,以消除铈量法在测定钼时产生的干扰。通过在钼标准中加入Ni试验证明,测定体系中存在大量Ni^2＋时,不干扰钼的测定。用草酸一硫酸联氨将Mo^6＋还原至Mo^5＋,用次甲基蓝作氧化促进剂,加快了滴定时的反应速度,终点突跃明显。拟定方法的样品加标回收率为95．0％～103．5％,相对标准偏差均〈1％。在实际测定中,方法快速准确,值得推荐。     

Determination of silver, antimony, bismuth, copper, cadmium and indium in ores, concentrates and related materials by atomic-absorption spectrophotometry after methyl isobutyl ketone extraction as iodides

Methods for determining ~ 0.2 mug g or more of silver and cadmium, ~ 0.5 mug g or more of copper and ~ 5 mug g or more of antimony, bismuth and indium in ores, concentrates and related materials are described. After sample decomposition and recovery of antimony and bismuth retained by lead and calcium sulphates, by co-precipitation with hydrous ferric oxide at pH 6.20 +/- 0.05, iron(III) is reduced to iron(II) with ascorbic acid, and antimony, bismuth, copper, cadmium and indium are separated from the remaining matrix elements by a single methyl isobutyl ketone extraction of their iodides from ~2M sulphuric acid-0.1M potassium iodide. The extract is washed with a sulphuric acid-potassium iodide solution of the same composition to remove residual iron and co-extracted zinc, and the extracted elements are stripped from the extract with 20% v v nitric acid-20% v v hydrogen peroxide. Alternatively, after the removal of lead sulphate by filtration, silver, copper, cadmium and indium can be extracted under the same conditions and stripped with 40% v v nitric acid-25% v v hydrochloric acid. The strip solutions are treated with sulphuric and perchloric acids and ultimately evaporated to dry ness. The individual elements are determined in a 24% v v hydrochloric acid medium containing 1000 mug of potassium per ml by atomic-absorption spectrophotometry with an air-acetylene flame. Tin, arsenic and molybdenum are not co-extracted under the conditions above. Results obtained for silver, antimony, bismuth and indium in some Canadian certified reference materials by these methods are compared with those obtained earlier by previously published methods.     

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.     

Extraktionsphotometrische Bestimmung von Zinn in molybdänhaltigen Stählen mit 3′-Pyridylfluoron

The steel sample is dissolved in a mixture of sulphuric acid and hydrogen peroxide. Tin is extracted as SnI₄ with benzene and determined photometrically with 3′-pyridylnuorone. 3×10^?4% of Sn can still be determined in a 1000 mg sample without interference of molybdenum. Standard deviations were within the range of ± 0.001 to ± 0.00002%.     

Extractive separation and spectrophotometric determination of tungsten as phosphotungsten blue

Phosphotungsten blue is produced by tin(II) reduction of tungstate solution complexed with phosphate at a w/w ratio of W/P = 5, in 4M hydrochloric acid medium, and extracted with isoamyl alcohol; thus tungsten is separated from Fe(III), Ni, Co, Cr(III), V(V), As(V), Sb(III), Bi, Si, U(VI), Ca and Cu(II). In presence of bismuth (0.5 mg/ml), 99.7% W is separated in a single extraction. After alkaline back-extraction, tungsten is determined spectrophotometrically as phosphotungsten blue; it is measured at 930 nm in aqueous solution or at 900-960 nm after isoamyl alcohol extraction, the Beer's law ranges being 0.08-0.6 and 0.16-0.72 mg/ml respectively. The methods are shown to give satisfactory results in the analysis of practical samples containing some milligrams of tungsten.     

Polarographic determination of uranium(VI) in aqueous tri-n-butyl phosphate solutions

The effect of TBP as well as the organic diluents on the polarographic wave of U(VI) reduction has been investigated in sulphuric and perchloric acids. It was found that the presence of TBP traces in the solution to be analyzed induced another wave which was more prominent in sulphuric acid solutions. This can be eliminated by boiling the solutions for about 5 min before their analysis for uranium. The effect of supporting electrolyte on the polarographic reduction of U(VI) was also studied and the use of 6N HClO₄ was recommended.     

Chromatographic separation of vanadium, tungsten and molybdenum with a liquid anion-exchanger

In acidic solution only molybdenum(VI), tungsten(VI), vanadium(V), niobium(V) and tantalum(V) form stable, anionic complexes with dilute hydrogen peroxide. This fact has been used in developing an analytical method of separating molybdenum(VI), tungsten(VI) and vanadium(V) from other metal ions and from each other. Preliminary investigations using reversed-phase paper chromatography and solvent extraction led to a reversed-phase column Chromatographic separation technique. These metal-peroxy anions are retained by a column containing a liquid anion-exchanger (General Mills Aliquat 336) in a solid support. Then molybdenum(VI), tungsten(VI) and vanadium(V) are selectively eluted with aqueous solutions containing dilute hydrogen peroxide and varying concentrations of sulphuric acid.     

Unified automated determination of silicon in iron ores, sinters, slags, iron and steel

An automatic absorptiometric method is presented for the determination of silicon in iron ores, sinters, slags, iron and steel. The last two are dissolved in dilute sulphuric acid; the others are fused with sodium peroxide, then dissolved in hydrochloric acid. After suitable additions and dilution, the resulting solutions are treated identically in a Technicon AutoAnalyzer. The silicomolybdate formed is reduced to molybdenum blue with iron(II). Fluoride is added to provide a redox buffering system. The novelty of the method lies in selecting the sample sizes, conditions of fusion and/or dissolution and dilutions so that this universality is attained. Thus a single programme for the analyzer serves to determine, in any sequence, silicon in iron ores or sinters (1-6%), slags (3-10%), iron (0.4-2.5%) or steel (0.005-2%), the only change being in the tables used to translate transmittanee into per cent silicon. Both the precision and accuracy are satisfactory.