Protactinium nitrates

No structural data are available for any of the pentavalent nitrates. Tetravalent protactinium nitrates are unknown. Fuming nitric acid oxidizes protactinium(IV) and obviously N.2O4 and N2O5 will do the same. However, it may be possible to prepare hexanitratoprotactinates(IV), M2Pa(NO j)a, or even complexes of the type Pa(N03)4>a L (L = oxygen donor ligand), analogous to those known for uranium(IV), by metatheses in nonaqueous solvents. 

In a study of the long-lived protactinium isotopes produced from thorium bombarded by high energy deuterons or helium ions (175), pieces of thorium metal of 25 mil thickness were used to increase the total yield of the protactinium. On the other hand, when the time for chemical separations had to be shortened in order to study the short-lived protactinium Isotopes, thinner pieces of thorium, 5 mils or less in thickness, were used to ensure rapid dissolution. In some cases, thorium nitrate powders wrapped in aluminum were used as the target in order to reduce further the time for dissolution of the target. 

Attempts to prepare protactinium pentanitrate by reacting penta-halides with liquid dinotrogen pentoxide have resulted in the formation of HPalNOglfl, possibly as a result of traces of anhydrous nitric acid present in the N Os 49). The presence of the jiroton has not been confirmed by electron spin resonance studies, but infrared results have shown that all the nitrate is covalently bound and vibrations associated with the nitronium and nitrosonium cations were not observed. Niobium and tantalum pentahalides react under similar conditions to form the anhydrous oxytrinitrates, M 0(N0g)3 20, 87). 

A few derivatives of oxyanions have also been prepared protactinium (V) forms hexanitrato complexes, Pa(N03)e , by reaction of the hexachloro complex with dinitrogen pentoxide, in contrast to niobium and tantalum which, under similar conditions, yield only tetranitrato complexes, M0(N03)4 (35). Neptunium (V) nitrates, NPO2NO3 and Np0(N03)3 have also been reported 71). Protactinium (V) sulfato-and selenato complex acids, H3PaO( 804)3 and H3Pa0(Se04)3, have been obtained from aqueous solution (13), but no fully sulfated or sele-nated species have been recorded. 

Protactinium can be recovered from an aqueous nitrate solution of fission products and protactinium by adding sodium chromate, which brings down protactiniiun on the aluminum chromate precipitate. After dissolution of the precipitate in acid, protactinium may be recovered by solvent extraction, or it may be allowed to decay to which is more easily extracted [G4]. Protactinium can also be recovered by adsorption on powdered Vycor glass. 

The thorium nitrate solution from the dissolver will be about 9 Af in nitric acid. To obtain satisfactory decontamination of thorium from fission-product protactinium, ruthenium, and zirconium-niobium, it was found necessary to remove all of the nitric acid from the solution and make the solution around 0.15 Af acid-deficient in nitrate ion by converting a fraction of the A1(N03)3 to a water-soluble basic nitrate. This also converts the readily hydrolyzed nitrates of these fission products to basic nitrates that are less extractable than the species present in the acid dissolver solution. 

Hyde and Wolf have studied the extraction of uranium and thorium by methyl n-amyl ketone and dllsopropyl ketone as a function of total nitrate concentration In the aqueous phase. In both cases, uranium was better extracted than thorium. The extraction of thorium did not become appreciable (<55 ) until the aqueous nitrate concraitratlon was greater than 5M. Dllsopropyl ketone was found to be an excellent extractant of protactinium. ... 

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