Molybdenum solvent extraction

In the determination of molybdenum in uranium alloys containing 2.5% molybdenum,20 the uranium had to be removed because its high absorbance made the method insensitive. After a single solvent extraction, the molybdenum could be determined with a standard deviation... 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Keywords Molybdenum (VI), 3-hydroxy-2- [-3- (4-methoxyphenyl)-l-phenyl-4-pyrazolyl]-4 -oxo - 4H-1-benzopyran, solvent extraction, spectrophotometry, determination... 

Tetra-n-heptylammonium iodide in benzene extracts TcO and MoO from an aqueous phase of pH 10.5. However, TCO4 is extracted much better. A separation factor of about 14 has been found. Thus, only a few cycles of solvent extraction are required to separate efficiently technetium from molybdenum . 

The determination of phosphorus after precipitation and solvent extraction as molybdophos-phoric acid (MPA) and reduction to molybdenum blue is a classical procedure,30 40 while cerium can be determined directly as molybdocerophosphoric acid (MCPA emax 7300 at 318 nm). A more selective method is to strip excess of MPA by extraction with chloroform, then to decompose residual MCPA and determine the phosphate liberated therefrom as MPA after extraction into isobutyl acetate. Alternatively AAS can be used to determine the amount of molybdenum. 

Since the solvent-extraction process is not selective for tungsten over molybdenum, any of the latter metal present is removed by the addition of sodium sulfide at a pH value of about 10... 

The technical-grade molybdenum(VI) oxide obtained as described previously can be further purified by solvent extraction as an alternative to the conventional sublimation method,216-217 the molybdenum being brought into solution by leaching of the oxide with sodium hydroxide ... 

Earlier atomic absorption methods [164-167] from the determination of molybdenum in soils employed a preliminary solvent extraction step to improve sensitivity in view of the low concentrations of molybdenum occurring in most soils. Baucells et al. [5] developed a graphite furnace atomic absorption procedure which was capable of determining down to 8.4 pg of molybdenum in a soil matrix solution with a precision of 4% for 100 pg/1 molybdenum. These workers showed that a char temperature of 1500 °C and an atomisation tem-... 

Thompson and Zao [170] have described a solvent extraction-inductively coupled plasma atomic emission spectrometric method for the determination of down to 0.02 - 0.03 xg/g of molybdenum in soils. The soil sample is pressure-leached with 6 M hydrochloric acid and at 120 °C for 15 minutes. The digest is then extracted with heptan-2-one to separate molybdenum from potentially interfering elements such as iron, aluminium, calcium and magnesium. This organic extract is then directly sprayed into an inductively coupled plasma atomic emission spectrometer operated at 1.65 to 1.7 kW power. 

UF6 Purification. Distillation of the UFfi is required for purification when the yellow cake does not go through solvent extraction. At Metropolis, the molybdenum, vanadium, and other impurities are removed in a pair of columns, one a 120-foot, 100-plate column operating at 200°F and 85 psia to remove the... 

The sample is wet digested, molybdenum is concentrated by chelation-solvent extraction, and determined by FAAS using a nitrous oxide-acetylene flame. 

H. Bergamin-Filho, J.X. Medeiros, B.F. Reis, E.A.G. Zagatto, Solvent extraction in continuous flow injection analysis. Determination of molybdenum in plant material, Anal. Chim. Acta 101 (1978) 9. 

A more complex but sensitive IC method was developed by Antony et al. based upon separation using a Dionex AS4A-SC column and postcolumn derivitization of phosphate using a solution containing 0.5% w/v ammonium molybdate and 0.5% w/v bismuth nitrate, in 1.75 M H2SO4 and 0.75% ascorbic acid. The resultant reduced ion association complex absorbed strongly at 700 nm and a detection limit for phosphate (P) of an impressive 0.8 /rg/1. The above chemistry has also been exploited in a recent publication by Haberer and Brandes " who carried out precolumn derivitization of phosphate within freshwater and saltwater samples and then solvent extracted the resultant molybdenum blue complex prior to separation and detection (at 700 nm) using reversed-phase HPLC. 

N. Trautmann, N. Kaffrell, H. W. Beuch, H. Folger, G. Herrmann, D. Hubscher and H. Ahrens, Identification of Short-lived Isotopes of Zirconium, Niobium, Molybdenum, and Technetium in Fission by Rapid Solvent Extraction Techniques, RadiocUm. Acta 18 (1972) 86. 

Chemical complexation already has become well established as a separation method in analytical chemistry and on a large scale in the applications of gas absorption and metals extraction. The ethanolamine and carbonate systems for removal of CO2 and H]S from gas streams are classic examples of complexation. Practical aspects of these systems are discussed in Chapter 6 and by Kohl and Riesenfeld, and the more theoretical aspects are discussed by Danckwerts, Danckwerts and Sharma, and Astarita et ai. In the metals industry, complexation is used extensively in the hydrometallurgical production of copper and uranium and in the refining of nickel, molybdenum, cobalt, and other metals for examples see Chapter 8 or the Proceedings of the triennial International Conferences on Solvent Extraction. 

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