The analysis of molybdates and tungstates

Abstract

Summary. The estimation of molybdenum and tungsten when present together has proved difficult, as is indicated by the large number of methods put forward for their determination. 1 Many of the methods given are for one or other of these elements only, a note often being added that the presence of the other invalidates the method. The estimation of molybdate and tungstate in the mineral powellite has been briefly described by one of the authors (A. A. M.) :2 molybdate and tungstate were precipitated as oxinates (Mo,W)O~(CgHsON)2 and the molybdate (MoO~") determined by measurement of the optical density at 230 m~ of a solution containing molybdate and tungstate. The amount of tungstate present was then estimated by difference. The property of the molybdate ion, MoO~", to absorb strongly in the ultra-violet has been further investigated and it has been found that, if a wave-length of 240 m/~ is chosen and the proper precautions taken, the MoO~" ion can be estimated without significant interference by the W04 '~ ion. Methods are given for the analysis of the common molybdate and tungstate minerals, together with results obtained during the course of this investigation.T HE analysis of molybdates and tungstates resolves itself into three parts: the separation of the anions from the cations, the estimation of the cations, and the estimation of the anions.The methods used to separate the anions from the cations and to estimate the cations depend on the nature of the nfineral but all methods yield a solution of sodium molybdate and sodium tungstate sensibly free from the mineral cations, and the method of analysis of the anions is the same for all minerals, a Experience has shown that, provided the conditions set out below, under scheelite, are followed, molybdate and tungstate can be precipitated together quantitatively, by means of oxine.A solution of sodium molybdate containing about 10 ppm MoO a shows no appreciable absorption above 275 m~. At wave-lengths less than this the absorption increases very rapidly but does not attain a maximum within the limits imposed by the instrument used (Unieam SP 500) : with similar concentrations of tungstate the absorption begins at much lower

Nonferrous metallurgy. II. Zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten

“…study of conditions (328) Methyl orange-H202: study of conditions (329) Reviews of spectrophotometric methods (367,388) CNS: Review (645); study of reduction methods (7,481,606) study of extraction (477,646); study of differential method (51); Nb (610); Ce (245); Se, Te (252); W, Al (604); steel (29,177,346,368,466); cadaver tissue (637); ores (8); flotation tails (596); molybdate salts (256); rock, soil, sediment (49) CNS-crystal violet: study of conditions (386) Toluene-3,4-dithiol: iron alloys (356); W (695); soils, sediments (734); water, silicates, biological materials (I46); sea water (630). Phosphotungstomolybdate: W (628,629) Mo(V): W, Ni, Cr, V, Mn, Cu (747) Mo04z~: minerals (192) K4[Fe(CN)e]: Re (748) EDTA: Nb (594) Tirón: electroplating baths (674) Thiosulfate: study of conditions (662) Thiomalic acid: Nb, Ti (595) Stilbazogall I: study of reagent and conditions (6I4) Pyrocatechol, Pyrocatechol-3,5-disulfonic acid: study of extraction (126) Pyrocatechol: Au (532) Zephiramine-CNS: study of extraction (487) Sulfosalicylic acid: refining catalyst (461) 1,10-Phenanthroline: study of conditions (458)_ Monothioglycol, unithiol: study of conditions and interferences (395) Morin: Ti, In, Ga (378); Cs, K, Na (253) 3-Phenyldaphnetin: study of conditions and interferences (323) Mercaptoacetic acid: steel (335,626) Sulfochlorophenol S: Zr, U, Fe (204,865) Diethyldithiocarbamate: study of conditions…”

“…Mo, A1 (685) H3BO3-HCI: Zr, Mo (599) Tamnin: minerals (591) Pyridine-2,5-dicarboxylic acid: study of conditions (171) Thioacetamide: study of conditions (122), steel, W (123) EDTA-Pb-Cr: study of reactions (538) -Benzoinoxime: W (403) Purpurogallin: Ti, Zr (188) Cupferron: Nb, A1 (685) 0-Naphthoquinone-tannin: W (686) Molybdiphosphates: study of reactions (59) 8-Hydroxyquinoline: Co (653) 8-Hydroxyquinoline: study of accuracy and precision (259); minerals (192) 0-Naphthoquinone + tannin: alloys (686) Variamine blue: steel (207) Pyramidon: sintered carbides (509) Acid dehydration-HCl: Ni, Al, S (573) 1,8-Naphthylenediamine: study of conditions (448) (201), and in tantalum (202). The 4-(2-pyridylazo)-resorcinol complex has also been found useful for the determination of niobium in steel (554) and zirconium (555) with no prior separation, and in steel following removal of the iron by extraction (733) and by ion exchange (166).…”

“…Tungsten, nickel, chromium, and vanadium do not interfere with the determination of molybdenum by the measurement of the absorbance at 305 mg of the molybdenum(V) chloride complex (747). Molybdenum was also determined by measuring the absorbance of the molybdate anion at 230 mg (192). Molybdenum formed complexes with ferrocyanide (748), EDTA (594), and thiosulfate (662) which could be used as the basis of spectrophotometric determinations.…”

“…Tungsten was determined in mixtures of tungsten and molybdenum by precipitating both with «-naphthoquinone and tannin, igniting to the oxide, and weighing and then redissolving and determining the molybdenum by a titrimetric procedure after which the tungsten was calculated by difference (686). In a similar procedure for the determination of tungsten in ores and minerals, both the tungsten and molybdenum were precipitated with 8-hydroxyquinoline, the molybdenum was determined by a spectrophotometric method, and the tungsten was then determined by difference (192). Tungsten in steel was determined gravimetrically by using variamine blue as the precipitant (207).…”

Polyoxometalate-Mediated Vacancy-Engineered Cerium Oxide Nanoparticles Exhibiting Controlled Biological Enzyme-Mimicking Activities

“…Phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) are electron-dense molecules and display quick and reversible multielectron redox reactions while maintaining their original structures. 40,41 They form larger oxoanions and are grouped under a category of polyoxometalates 42,43 and utilized in a wide range of industrial applications. 44 Structurally, they have a tetrahedral framework consisting of a central molybdenum or tungsten atom surrounded by four oxygen atoms.…”