Protactinium sulfates

Although it is known that protactinium(V) precipitates from dilute sulfuric acid on the addition of potassium sulfate, the product, believed to be K3Pa0(S04)3, has not been satisfactorily characterized (19, 28, 105). There is obviously scope for further research on the preparation of sulfato (and selenato) complexes of pentavalent protactinium. In addition, tetravalent protactinium sulfates, selenates, and their complexes have not been studied. 

Protactinium is separated by solvent extraction and anion exchange processes by using sulfate solutions. After chemical separation, the protactinium salts are ignited to a pentoxide, Pa205, which may be converted into an arsenazo(III) complex. The absorbance of the solution is measured at 630 nm with a spectrophotometer. Protactinium-231 is an alpha emitter and also forms photons at 300 KeV, which can be measured by various radioactive counters and spectrophotometric techniques. Protactinium also can be measured by neutron activation analysis. 

Pentavalent. Protactinium is known to bind sulfate in solutions of H2SO4 however, very limited data are available on the molecular species. Sulfate complexes with the general formula of Np02(S04) " (n = 1 3) have been reported. In most of these complexes, the Np is found in a seven-coordinate pentagonal bipyramid geometry. 

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. 

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