Tungsten separation from molybdenum

Dimethyl sulfoxide has found application as a solvent for electrochemical studies of Mo(VI) and Mo(V) complexes of quinol derivatives (287). Sulfoxides have also been examined as extractants for the separation of molybdenum and tungsten from acid solutions (218). 

Bradfield and Stickland [40,41] determined molybdenum in plant tissue by its catalytic effect on the liberation of iodine from the reaction between potassium iodide and hydrogen peroxide. The detection limit is 0.003 pg/ml of molybdenum. Interference from iron and tungsten can be overcome by addition of ammonium fluoride, but for the greatest precision and accuracy a preliminary separation of molybdenum as its benzoin a-monoxime complex is recommended. 

The metal values associated with other minerals but not amenable to separation and concentration by the standard beneficiation techniques such as flotation can usually be recovered by chemical methods. The Climax Molybdenum process to recover the molybdenum oxide values associated with the sulfide ore and the Union Carbide process for the separation of molybdenum from tungsten in a floatation concentrate are in this category. 

Tlie only other metals likely to give a blue colour are columbium, vanadium, motybdenum, and titanium. The colour due to columbium disappears on dilution. The colour due to vanadium may be obtained by means of tartaric acid, which gives no colour with tungsten. The colour formed on reduction of molybdenum is from iolet to black, while that due to titanium is iolet these elements can easily be separated from the tungsten before the reduction test is made. ... 

Kim BM, Process for separation of molybdenum from tungsten leachate, US Patent 4,443,414, 1984. 

Molybdenum and tungsten were quantitatively separated from sea water by the addition of H2O2 and NH4SCN in 0.1 M HCl (for Mo) at a cation-exchange resin ). Elution followed with 0.5 M NaOH/0.5 M NaCl. 

Toluene-3,4-dithiol (dithiol 30) gives complexes with many metals (e.g. Bi, Sb , Co, Cu, Ni and Pb in acid solution Mn, Fe, Tl, V and Ru in alkaline, aqueous pyridine solution). The yellow-green tris complex with molybdenum can be separated from tungsten(VI) by extraction into pentyl acetate from 3.7 M HCl. The blue-green tungsten complex extracts if the acidity is lowered. Sn also gives a yellow-red complex. 

Molybdenum and tungsten. Oura et al. (2007) apphed postirradiation RNAA to determine trace amounts of Mo and W in geo- and cosmochemical samples. Samples were fused and Mo and W were separated from other elements by an anion resin. Chemical recoveries were determined by ICP-OES for both elements in each sample. To correct the Mo results for fissiogenic Mo resulting from fission of another fission product, i.e., I in each sample solution was determined by RNAA. Iodine was separated as Pdia precipitate. Under the given experimental conditions, detection limits of about 100 ppb for Mo and W were achieved. 

S. Fritz and L. H. Dahmer, Cation exchange separation of molybdenum, tungsten, niobium and tantalum from... 

Reduction to Solid Metal. Metals having very high melting points caimot be reduced in the Hquid state. Because the separation of a soHd metallic product from a residue is usually difficult, the raw material must be purified before reduction. Tungsten and molybdenum, for instance, are prepared by reduction of a purified oxide (WO, MoO ) or a salt, eg, (NH2 2 G4, using hydrogen. A reaction such as... 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

If tungsten is recovered from the wolframite group mineral, the wolframite concentrate is boiled or pressure-digested with 50% caustic soda solution. Alternatively, they may be fused or sintered with caustic soda, caustic potash or sodium carbonate and the fused mass then leached with water. The solution is filtered to separate sodium tungstate solution. The fdtrate is subjected to various treatments to remove molybdenum, phosphorus, and arsenic impurities. The filtrate at this point is essentially a solution of sodium tungstate and is treated in the same way as that obtained from the scheehte concentrate discussed above. 

A general method for the separation of vanadium from arsenic, molybdenum, phosphorus, chromium, uranium, tungsten, and silicon, consists in precipitating these metals as their respective lead salts and digesting the precipitate with potassium carbonate, whereupon all the lead salts are decomposed with the exception of the lead vanadate.5... 

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