The Chemistry of Protactinium. IV : On the Absorption Spectra of Tetravalent Protactinium in Aqueous Solutions

The liquid zinc amalgam method was developed as a rapid procedure for the reduction of pentavalent protactinium. Several minutes were sufficient for the complete reduction of 4.2×10^M pentavalent protactinium in both hydrochloric and sulfuric acid solutions. The stability of tetravalent protactinium in these media was investigated by spectrophotometry. Re-oxidation occurred gradually, even in the absence of atmospheric oxygen, and amounted to 8% in 15 hr. These results may be understood in terms of the slow rate of the (chemical formula) reaction. The formation of sulfato complexes of tetravalent protactinium was inferred by spectrophotometry with relation to the similarity of the electronic structure between Pa^(5f^1) and Ce^(4f^1)