U
6+ can be separated from U
4+ as the latter gives precipitate with (NH
4)
2CO
3. Heretofore, the separation of U from Fe is carried out with the use of (NH
4)
2CO
3 or cupferron and this method is to precipitate out the Fe, but it is unsuitable to apply on sample containing large amount of Fe and small amount of U, on the other hand, reduction of Fe
3+ to Fe
2+ and U
6+ to U
4+ causes the precipitation of U with (NH
4)
2CO
3 and these are separated each other. In the gravimetric estimation of U by precipitation with the addition of NH
4OH, the formation of precipitate is not possible unless large quantities of NH
4Cl is added, while the formation of precipitate is not possible unless large quantities of NH
4Cl is added, while the formation of precipitate is possible without NH
4Cl when U
6+ is previously reduced to U
4+. Since U
4+ is oxidizable on heating in the presence of air, its titration with KMnO
4 should be carried out below 25°C. Dissolving of U
3O
8 (or 2UO
3·UO
2) in a solution of NH
4VO
3 in H
2SO
4 in the presence of air causes the reduction of V
5+ by U
4+ to V
4+ which is stable in the presence of air and titrable with KMnO
4 solution, therefore, volumetric estimation of U
3O
8 is possible.
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