Vanadium chromates

The vanadium chromates have been discussed in connection with the chromium vanadates. According to C. W. Blomstrand, an aq. soln. of columbium oxychloride gives a yellow, granular precipitate of columbium chromate when it is treated with potassium chronoate. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

A. M. del Rio in 1801 claimed to have discovered the previously unknown element 23 in a sample of Mexican lead ore and, because of the red colour of the salts produced by acidification, he called it erythronium. Unfortunately he withdrew his claim when, 4 years later, it was (incorrectly) suggested by the Frenchman, H. V. Collett-Desotils, that the mineral was actually basic lead chromate. In 1830 the element was rediscovered by N. G. Sefstrom in some Swedish iron ore. Because of the richness and variety of colours found in its compounds he called it vanadium after Vanadis, the Scandinavian goddess of beauty. One year later F. Wohler established the identity of vanadium and erythro-nium. The metal itself was isolated in a reasonably pure form in 1867 by H. E. Roscoe who reduced the chloride with hydrogen, and he was... 

It is evident from Fig. 22.2 that only in very dilute solutions are monomeric vanadium ions found and any increase in concentrations, particularly if the solution is acidic, leads to polymerization. nmr work indicates that, starting from the alkaline side, the various ionic species are all based on 4-coordinate vanadium(V) in the form of linked VO4 tetrahedra until the decavana-dates appear. These evidently involve a higher coordination number, but whether or not it is the same in solution as in the solids which can be separated is uncertain. However, it is interesting to note that similarities between the vanadate and chromate systems cease with the appearance of the decavanadates which have no counterpart in chromate chemistry. The smaller chromium(VI) is apparently limited to tetrahedral coordination with oxygen, whereas vanadium(V) is not. 

Discussion. Small amounts of chromium (up to 0.5 per cent) may be determined colorimetrically in alkaline solution as chromate uranium and cerium interfere, but vanadium has little influence. The transmittance of the solution is measured at 365-370 nm or with the aid of a filter having maximum transmission in the... 

Molybdenum(VI), vanadium(V), mercury, and iron interfere permanganates, if present, may be removed by boiling with a little ethanol. If the ratio of vanadium to chromium does not exceed 10 1, nearly correct results may be obtained by allowing the solution to stand for 10-15 minutes after the addition of the reagent, since the vanadium-diphenylcarbazide colour fades fairly rapidly. Vanadate can be separated from chromate by adding oxine to the solution and extracting at a pH of about 4 with chloroform chromate remains in the aqueous solution. Vanadium as well as iron can be precipitated in acid solution with cupferron and thus separated from chromium (III). 

The effects of various metal oxides and salts which promote ignition of amine-red fuming nitric acid systems were examined. Among soluble catalysts, copperQ oxide, ammonium metavanadate, sodium metavanadate, iron(III) chloride (and potassium hexacyanoferrate(II) with o-toluidine) are most effective. Of the insoluble materials, copper(II) oxide, iron(III) oxide, vanadium(V) oxide, potassium chromate, potassium dichromate, potassium hexacyanoferrate(III) and sodium pentacyanonitrosylferrate(II) were effective. 

Dr. Ernst Wittich, German Ambassador to Mexico, pointed out that Baron von Humboldt was also led into the same error, for the specimen in the Museum fur Naturkunde in Berlin is labeled in the Baron s handwriting Brown lead ore from the veins of Zimapin in northern Mexico. Lead chromate. M. del Rio thought he had discovered a new metal in it, which he named erythronium, then panchromium later he realized that it was ordinary chromium. The label was later corrected by Gustav Rose to read Vanadiumbleierz (vanadium lead ore) (29). 

Normal chromates of vanadium have not been prepared. An ammonium vanadochr ornate, 2(NH4)2O.V808.2Cr03.7HaO, has been prepared in red crystals by dissolving vanadium pentoxide in ammonium chromate solution and evaporating at ordinary temperatures in vacuo.6... 

Gravimetric Methods.—The vanadium compound is converted into sodium vanadate by fusion or other method, and after separation from other salts (e.g. arsenate, molybdate, phosphate, chromate, tungstate) is precipitated from nearly neutral solution either as (a) mercurous vanadate or (b) basic lead vanadate. In (a), mercurous... 

Silver, copper and other oxosalts have been extensively studied as cathodes in laboratory cells commercial power sources, principally for pacemakers, using silver chromate were manufactured until the 1980s, and silver vanadate or silver vanadium oxide (Ag2V4On), first reported by workers at Wilson Greatbatch Ltd, is currently used as cathode in implantable cardiac defibrillator batteries. 

VANADINITE. The mineral vanadimte corresponds to the formula Pb VO Cl, being composed of lead chloride and lead vanadate in the proportion of 90.2% of the former and 9.8% of the latter. It crystallizes in the hexagonal system, is usually prismatic, but the ciystals are often skeletal or cavernous it may be found in crusts. Its fracture is uneven brittle hardness. 2.75-3 specific gravity. 6.86 fresh fractures show a resinous luster color, yellow, yellowish-brown, reddish-brown, and red streak, white to yellowish translucent to opaque. Vanadinite, not a common mineral, occurs as an alteration product in lead deposits. It is found in the Ural Mountains, Austria, Spain, Scotland, Morocco, the Transvaal, Argentina, and Mexico, In the United States it occurs in Arizona, New Mexico, and South Dakota, It is used as an ore of vanadium and to some extent of lead as well. It is interesting to note that this mineral was first described as a chromate upon its discovery in Mexico in 1801, It was not until the discovery of the element vanadium in 1830 that the true nature of this compound was known. 

Lead was found frequently at the 0-10 /xg/cm2 level in many old papers, possibly picked up from processing equipment. The wt % of the 325 /xg/cm2 of lead as the chromate, PbCr04 (8), found in the Amies yellow paper, basis weight 0.92 g/dm2, is 325/0.92 X 01 = 3.5%. Antimony appeared randomly at the 0-2-/xg/cm2 level. Other elements found but not plotted were titanium, cerium, cesium, gallium, mercury, rubidium, strontium, vanadium, yttrium, and zirconium. 

In the external environment of tunicates, most metal ions are cationic, few are anionic. Vanadium is one of the anions, as it is present predominantly as HzVOj at the pH of sea water. Only chromate, among the metal-containing anions, is significant in sea water and it is present at a fiftieth the concentration of vanadium8. Other anions to consider are sulfate and phosphate, present as SO4 and HPO4" in sea water. 

POTASSIUM TRIIODIDE see PLW285 POTASSIUM TROCLOSENE see PLDOOO POTASSIUM, metal aUoys pN 1420) pOp see PKT250 POTASSIUM VANADIUM TRIOXIDE see PLK810 POTASSIUM ZINC CHROMATE see PLW500 POTASSIUM ZINC CHROMATE see CMK400 POTASSIUM ZINC CHROMATE FIYDROXIDE see PLW500... 

Certain systems which behave reversibly in the equilibrium state exhibit considerable polarization in the course of electrolytic reduction examples are the conversion of 5-valent vanadium to the 4-valent state, and of the latter to the 3-valent condition, the reduction of 6- to 5- and of 5- to 3-valent molybdenum, and the reduction of 6-valent to 5-valent tungsten. There is reason to believe, however, that in all these cases the abnormal behavior is to be attributed to the presence of oxide films on the cathode by producing a partial blocking of the surface, these oxide films increase the effective c.d., so that the potential rises. Considerable polarization, accompanied by oxide-film formation, occurs in the reduction of chromate to chromic ions, but it is not certain how far this system is reversible. 

There is brief mention of some iodide-induced exchange of bromate oxygen If correct, this would imply that the rate is limited by (13) or (16). Since, in the reaction with sulphite"the sulphate formed takes oxygen from bromate, that reaction is related to (14), not to (11). In addition to catalysis by chromate , vanadium(V) has been shown to be effective . When oxalate is also present, radicals appear to be produced , as shown by polymerization of acrylonitrile. Vanadium(VI) is suggested as an intermediate . This is of some interest since most authors have regarded one-electron oxidation steps in this whole class of reactions as highly improbable. 

Weak complexes form between vanadate and phosphate, 9,99 pyrophosphate,59 arsenate,59 and chromate.106 The formation constant for the simple phosphovanadate is about 20 M 1." Structural characterization has been reported for interesting cluster structures of vanadium with organophosphonates107 and with sulfate.108 Divanadium(V) complexes with either monodentate or bidentate nitrate (N03 ) groups have been reported.109... 

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