Nitric acid from molybdenum

Wet Tests.— When hydrogen sulphide is passed through an acidified solution containing molybdenum, the trisulphide is thrown dowm. The precipitate dissolves in ammonium sulphide, and it is therefore in ordinary analysis separated with the Group IIb metals, namely, arsenic, antimony, tin, gold, and platinum. The last four metals may be precipitated by addition of metallic zinc, the arsenic expelled by evaporation, and, after taking to dryness with nitric acid, the molybdenum may be extracted from the residue with ammonia. The trisulphide may be reprecipitated directly by the addition of nitric acid to the solution in ammonium sulphide. A soluble sulphide added to a solution of ammonium molybdate gives a blue colour. 

Phosphorus from organophosphorus compounds, which are combusted to give mainly orthophosphate, can be absorbed by either sulphuric acid or nitric acid and readily determined spectrophotometrically either by the molybdenum blue method or as the phosphovanadomolybdate (Section 17.39). 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

In a method described by Kiriyama and Kuroda [500], molybdenum is sorbed strongly on Amberlite CG 400 (Cl form) at pH 3 from seawater containing ascorbic acid, and is easily eluted with 6 M nitric acid. Molybdenum in the effluent can be determined spectrophotometrically with potassium thiocyanate and stannous chloride. The combined method allows selective and sensitive determination of traces of molybdenum in seawater. The precision of the method is 2% at a molybdenum level of 10 xg/l. To evaluate the feasibility of this method, Kiriyama and Kuroda [500] spiked a known amount of molybdenum and analysed it by this procedure. The recoveries for 4 to 8 xg molybdenum added to 500 or 1000 ml samples were between 90 and 100%. 

The chromatographic separation of technetium from molybdenum is based on the different extent to which molybdate and pertechnetate are adsorbed from alkaline and acid solutions. The distribution coefficient of molybdate between the anion exchanger Dowex 1-X8 and 3 M NaOH is 12, while it is 10 for pertechnetate under the same conditions. Molybdate is also adsorbed to a much lesser extent from hydrochloric acid solutions than pertechnetate. Thus, molybdemun can be eluted by hydroxide or HCl solutions while nitric acid, perchlorate or thiocyanate are used for the elution of technetium . 

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

Tucker et al. have separated " Tc from the fission product Mo using chromatographic aluminum oxide washed by dilute nitric acid at pH 1.5. Mo dissolved in the same dilute HNO3 of pH 1.5 is passed through the column which is then eluted with 0.1 M HNO3. Tc is only slightly adsorbed and can easily be eluted while molybdenum is retained on the column. The purity of technetium is 99.99%. 

Elemental composition Mo 45.70%, F 54.30%. The compound may be identified from its physical properties. Molybdenum may be analyzed by AA or ICP in an acid extract of the compound following digestion with nitric acid. 

An alternative method involves repeatedly evaporating a mixture of ammonium molybdate and nitric acid. Ammonium nitrate so formed is separated from the product molybdenum(VI) oxide by extraction with water ... 

Elemental composition Mo 35.12%, Cl 64.88%. Molybdenum pentachloride may be identified from its physical properties and the products it forms in various reactions. The molybdenum content may be measured by flame or fur-nace-AA or ICP/AES measurement following digestion with nitric acid and appropriate dilution. 

C6H5C1, is produced commercially in the liquid phase by passing chlorine gas into benzene in the presence of molybdenum chloride at 30—50°C and atmospheric pressure. This continuous process yields a 14 1 ratio of chlorobenzene to dichlorobenzene [106-46-7], C6H4C12. The reaction ofiodine with benzene takes place only in the presence of oxidizing agents such as nitric acid. Iodobenzene [591-50-4], C6H5I, is thus produced from reaction of benzene,... 

Fujii, T., Yamana, H., Watanabe, M., Moriyama, H. 2001. Extraction of molybdenum from nitric acid by octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide. Solvent Extr. IonExch. 19 (1) 127-141. 

Recoveries of molybdenum obtained by the nitric acid-hydrogen peroxide digestion procedure ranged from 96.4 2.9% for lettuce to 100.9 5.4% for beet leaves compared to 101.1 5.2% for lettuce to 98.8 4.95 for beet leaves obtained by dry oxidation. Recoveries obtained for reference plant materials are listed in Table 7.3. 

There is distinct evidence that much-improved recoveries of cobalt and molybdenum from grains and grass can be obtained by using nitric acid in conjunction with potassium, hydrogen sulfate or sulfuric acid ashing acids and oxygen enrichment. 

Molybdenum. Molybdenum can be analyzed by P CAM 173 for total Mo, by S-193 (12) for soluble Mo, or by S-376 for insoluble Mo. The standard nitric wet ashing used in P CAM 173 does not distinghish between soluble and insoluble Mo which have OSHA standards of 5 mg/cu m and 15 mg/cu m. Nitric acid digestion may not dissolve some insoluble Mo that require nitric/perchloric acid or base/nitric acid depending on the solubility properties. Soluble Mo compounds are hot water leached from the cellulose membrane filter used in all three methods. A fuel-rich air/acetylene flame used in P CAM 173 is replaced by an oxidizing nitrous oxide/acetylene flame to achieve total atomization of Mo as detected at 313.3 nm. Aluminum and traces of acid enhance the Mo flame response therefore, 400 ppm A1 is added to the final solution of both S-193 and S-376 and 0.1 N nitric acid is added to the water leach-soluble Mo final solution, S-193. 

After irradiation of the uranium target, it is dissolved in nitric acid and the final solution adsorbed on an alumina column that is washed with nitric acid to remove uranium (and other fission products). Molybdenum is finally eluted with ammonium hydroxide and further purified by absorption on an anion exchange column from which ammonium molibdate is eluted with dilute hydrochloric acid after washing the resin with concentrated HC1. The "Mo is obtained in no-carrier-added conditions, and the most common contaminants can be 131I and 103Ru. 

Molybdenum(IV) oxide (Mo02), is obtained by reducing Mo03 with hydrogen or NH3 below 470°C (above this temperature reduction proceeds to the metal) or by reaction of molybdenum with steam at 800°C. It is a brown-violet solid with a coppery luster, insoluble in nonoxidizing mineral acids but soluble in concentrated nitric acid with oxidation of the molybdenum to Movr. The structure is derived from that of rutile but distorted so that strong Mo—Mo bonds are formed. Tungsten dioxide is similar. Mo—Mo and W—W distances are 2.51 and 2.49 A, respectively. 

Fundamental studies have been reported using the cationic liquid ion exchanger di(2-ethylhexyl) phosphoric acid in the extraction of uranium from wet-process phosphoric acid (H34), yttrium from nitric acid solution (Hll), nickel and zinc from a waste phsophate solution (P9), samarium, neodymium, and cerium from their chloride solutions (12), aluminum, cobalt, chromium, copper, iron, nickel, molybdenum, selenium, thorium, titanium, yttrium, and zinc (Lll), and in the formation of iron and rare earth di(2-ethylhexyl) phosphoric acid polymers (H12). Other cationic liquid ion exchangers that have been used include naphthenic acid, an inexpensive carboxylic acid to separate copper from nickel (F4), di-alkyl phosphate to recover vanadium from carnotite type uranium ores (M42), and tributyl phosphate to separate rare earths (B24). 

Iron-chromium alloys, free from carbon, may be prepared from chromite by the alumino-thermic method. From a study of the cooling-and freezing-point curves it has been suggested that a compound, Cr Fe, exists, but this is questioned by Janecke, who studied the iron-chromium system by means of fusion curves and by the microscopic study of polished sections of various alloys between the limits 10 Fe 90 Cr and 90 Fe 10 Cr, and came to the conclusion that the system consists of a single eutectic which can form mixed crystals with either component. The eutectic contains 75 per cent, of chromium and melts at 1320° C. The addition of chromium to iron increases the readiness of attack by hydrochloric and sulphuric acids, but towards concentrated nitric acid the alloys are rendered passive. They remain bright in air and in water. The presence of carbon increases the resistance to acids and renders them very hard if carbon-free, they are softer than cast iron. All the alloys up to 80 per cent, chromium are magnetic. Molybdenum, titanium, vanadium, and tungsten improve the mechanical properties and increase the resistance to acids. 

Preparation.—Although the purest molybdenum is obtained from wulfenite, the chief commercial source is molybdenite, which is converted into the trioxide by roasting in air either with or without the addition of sand, and, on dissolving the residue in ammonia, a solution of ammonium molybdate is obtained. This salt, freed from copper by treatment in ammoniacal solution with ammonium sulphide, and from aluminium by the addition of potassium carbonate, on ignition yields molybdenum dioxide alternatively, heating with excess of sulphur yields pure molybdenum disulphide, MoS, which on roasting, or by treatment with nitric acid, is converted into the trioxide MoOj. ... 

From wulfenite, molybdenum trioxide is prepared by digesting the mineral (previously washed with dilute hydrochloric acid) with concentrated hydrochloric acid lead still remaining in solution after cooling and filtration is removed by the addition of sulphuric acid, and the filtrate is evaporated to dryness with the addition of a small quantity of nitric acid. The ammonia extract of this mass is then subjected to the method of purification previously described. Another method consists in decomposing the finely powdered mineral by means of concentrated sulphuric acid, diluting to precipitate lead sulphate, and evaporating the filtrate until precipitation of molybdic anhydride occurs. ... 

Sodium Trimolybdate, NaoMOgOjo-fPlTHgO. crjstallises from a saturated solution of molybdenum trioxide in sodium carbonate,or from such a solution treated with a suitable excess of nitric acid or it may be obtained by the addition of a large excess of acetic acid to a solution of the paramolybdate.The trimolybdate yields fine needles which at 100° C. lose 6HjO it is rather more soluble in hot than in cold water. 

A method, suitable for the analysis of molybdates and molybdenum ores, consists in heating the substance at 400° to 560° C. in a stream of carbon tetrachloride vapour, when molybdic acid volatilises and may be collected in a receiver, evaporated with nitric acid, ignited, and weighed. If iron is present it also volatilises, and must be separated from the condensed product. 

Molybdenum(VI) sorption was achieved on Sephadex G-10 at pH 2.5 in ammonium chloride solutions by the formation of a M0-NH3-glucose complex Alkali- and alkaline earth metal traces remained quantitatively in the effluent and were determinable with a coefficient of variation of 10% up to 60 ppm, and 5% at above 60 ppm. Uranium was separated from rare-earth elements using a cellulose column and an ether-nitric acid separation procedure... 

The precipitation of the zirconium-molybdenum material is a function of acid strength, temperature and time. The rate of precipitation is lower with lower temperatures, low zirconium concentrations and higher acid strengths. There also appears to be an induction period before the onset of precipitation. Discussed here is the characterization of the zirconium molybdate solids, as obtained separately from nitric acid solutions chemical analyses, thermogravimetry and X-ray powder diffraction were used to characterize these solids. 

In the absence of zirconium, a plutonium-molybdenum compound can be precipitated from nitric acid solutions. The presence of zirconium in the same solution is detrimental to formation of this material, as zirconium molybdate is formed preferentially. However, the amount of Pu molybdate solids that form is a function of hydrogen ion concentrations at 1M HN03 or less, solids form but at higher acid concentrations the quantity of precipitate decreases. At 3M HN03 solids are just barely detectable. 

The plutonium-bearing precipitate obtained from nitric acid solutions (containing molybdenum, zirconium and plutonium) gives an X-ray powder diffraction pattern not distinguishable from that of ZrMo207(0H)2(H20)2 precipitated without plutonium. However, since the Pu content is low, the Pu could be present either in the Pu molybdate structure or replacing Zr in the Zr molybdate structure and not be detected in the X-ray patterns. 

---