Spectroscopic study of the uranyl hydrolysis species (UO2)2 (OH) 2 2+

The behavior of (UO₂)₂(OH)₂²⁺ has been investigated in solid-liquid equilibria under 100%, 8%, 1%, 0.3% and 0.03% CO₂ partial pressure as well as in undersaturated systems in equilibrium with air at 24±2°C in 0.1M NaClO₄ solutions. From spectroscopic investigations by UV-Vis-and time-resolved laser-induced fluorescence (TRLF) spectroscopies, single component absorption and emission spectra are suggested for the (UO₂)₂ (OH)₂²⁺ species. The lifetime ₂₂ of the fluorescence emitting electronically excited state of (UO₂)₂(OH)₂²⁺ was determined as ₂₂ = 2.9 ± 0.9 s. The formation constant of (UO₂)₂(OH)₂²⁺ was found to be log K₂₂=–5.97 ± 0.06. Interpretation of the experimental data was also made assuming the species (UO₂)₂(OH)₂²⁺, but unsatisfactory results have been obtained.