Formation and stability of PU(IV) colloids in aquatic solution

The chemical reactions of aquatic Pu(IV) in dilute concentrations are of cardinal relevance for the appraisal of its thermodynamic solubility. Spontaneous colloid formation and disproportionation reactions hinder a straightforward approach and lead to a large number of controversial results in the past. The present work describes a combination of several complementary methods to investigate the solubility of Pu(IV) as a function of pH. At first, laser-induced breakdown detection (LIBD) was applied for colloid quantification. Its sensitivity is higher than photon correlation spectroscopy (PCS) by 7 orders of magnitude (for colloids smaller than 50 nm) and applicable down to 5 nm-particles. To obtain optical absorption spectra for speciation a new diode array spectrometer with a 1m capillary cell (550 μm in diameter), which is 100 times more sensitive than a normal spectrometer, was applied. Its detection limit for Pu(III) and Pu(IV) is below μM. Additionally the capillary electrophoresis (CE) coupled with ICP-MS was used for speciation. (orig.)