Molybdenum precipitates from nitric acid

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 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. 

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. 

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. ... 

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. 

I. From molybdenite, the extraction may be made in several ways, (a) The mineral is roasted as long as sulfur dioxide is given off. The residue which contains MoOs is leached with dilute ammonia and the solution evaporated until the ammonium molybdate crystallizes. Japanese patent 37420 (1920) extracts the roasted ore with Na2COj solution, then precipitates calcium molybdate by adding CaCb. (6) The finely ground ore is heated with nitric acid and the MoOj dissolved in ammonia, (c) A current of chlorine is passed over the dry pulverized ore at a temperature of 208°. The molybdenum chloride distills over and may be separated from sulfur and other chlorides by fractional condensation.2 (d) A British patent describes the extraction with an alkaline sulfide or polysulfide solution which removes the molybdenum from the ore as the soluble thio-molybdates. These may be converted to the molybdates by acidification or by contact with more ore. 

Remove the Nitric Acid Test from ASTM A 262 and establish it as a separate ASTM Test At present, the boiling 65 % nitric acid test (Practice C) is specified for materials to be used in nitric acid service. Only this test is sensitive to sigma-phase in molybdenum-bearing austenitic stainless steels. Also, problems such as end-grain corrosion associated with hexavalent chromium derived from corrosion products are unique to this solution. While this test also detects susceptibility to intergranular attack associated with chromium carbide precipitates, there are other tests that perform this function in less time and with greater simplicity. 

The nitrosyl carbonyls CpM(NO)(CO)2 [M=Cr (21, 7S), Mo (57), W (19)) can be made by the action of nitric oxide on [CpCr(CO)3]2, [CpMo(CO)3] , or [CpW(CO)3] , respectively. The chromium complex undergoes a Friedel-Crafts acetylation to give (CsH4COCH3)Cr(NO)(CO)2 (21). A series of molybdenum complexes CpMo(NO)l2L [L = PPh3, P(OPh)3, py, and bipy] has been made from L and [CpMo(NO)l2]2 (57). The cationic manganese species [CpMn(NO)(CO)2], obtained by the action of nitrite and acid on CpMn(CO)3, can be precipitated as the yellow hexafluorophosphate salt (51). With sodium borohydride this affords [CpMn(NO)(CO)]2 which probably contains bridging NO groups (see below) (58). The complex [CpMn(NO)S2] is probably similar in structure... 

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