Hydrolysis of plutonium(IV) in acidic solutions: no effect of hydrolysis on absorption-spectra of mononuclear hydroxide complexes

Tetravalent plutonium readily undergoes hydrolysis even in highly acidic aqueous solutions. In the past, many attempts were made to quantify hydrolysis species by means of optical absorption spectroscopy. In the present work solutions ranging from 10 −5 M to 10 -2 M (total Pu) concentration in 0.5 M HCl/NaCl (0.3 < pH c < 2.1) are carefully investigated by combining absorption-spectroscopy (UV-Vis, liquid core waveguide capillary) and laser-induced breakdown detection, with special emphasis on the limited solubility of Pu(IV). The results clearly indicate that all changes in the absorption spectra originate from the formation of Pu-polyspecies and colloids. The molar absorptivity of mononuclear Pu(IV) hydroxide complexes does not vary with increasing pH c and ongoing hydrolysis. The normalized absorption spectra of at least the first and the second hydroxide complex (Pu(OH) n 4- n n = 1, 2) do not differ from those of the hydrated Pu 4+ ion.