Uranyl hydroxide / Uranyl carbonate j Solubility products / Complexation SummaryThe solubility of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the supematant Solution were determined at 25°C in 0.1 M NaClOi solutions. The solubility products were found to be logA^,p= -22.21 and log/Csp= -13.29. respectively. In the pH ränge from 4.5 to 5.5 the hydroxo complexes (U02)2(0H)r (lg/? = 22.16), and (U02)3(0H)5^ (lg^ = 53.05) were found. Under the condition -11

The rate at which elements can be transported in groundwater systems is governed in part by the solubility of the element in the groundwater. This report documents plutonium solubility experiments, conducted over the past two years at the Lawrence Berkeley Laboratory, in a brine simulant relevant to the Waste Isolation Pilot Plant. Approximately 1 to 2.5 mL of five stock solutions containing single oxidation states of plutonium (Pu(IV)-polymer, Pu 3+ , Pu 4+ , Pu0 2 + , and PuOD were added to -75 mL of synthetic H-17 Brine in five reaction vessels. Initial plutonium concentrations ranged from 1.3 X10 4 to 5.1 Χ10" 4 Μ (moles per liter) total plutonium. Because these initial concentrations were far above the plutonium solubility limit in H-17 Brine, plutonium-containing solids precipitated. Aqueous plutonium concentrations were measured over time until steadystate was reached, requiring over 300 days in H-17 Brine. Steady-state plutonium concentrations ranged from 3.0 X 10~8 to 7.6 X 10~7 M, and the predominant plutonium oxidation state in solution was Pu(VI). The solid phase from the initially Pu(IV)polymer experiment remained polymeric-Pu(IV). The solids that formed in the initially Pu 3+ and Pu 4+ experiments were crystalline yet remain unidentified. The solids that formed in the initially Pu0 2 + and PuOi + experiments appear to be sodium plutonyl(V) carbonates.

The rate at which elements can be transported in groundwater systems is governed in part by the solubility of the element in the groundwater This report documents plutonium solubility experiments, conducted over the past two years at the Lawrence Berkeley Laboratory, in a brine simulant relevant to the Waste Isolation Pilot Plant Approximately 1 to 25 mL of five stock solutions containing single oxidation states of plutonium

The solubility products of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the solution have been determined at 25°C and I=0.1 mol dm" 3 by potentiometry and solubility experiments. The uranyl complexes U0 2 (OH) 2 , (UO2) 2 (OH)2+, (UO2) 3 (OH) 5 +, U0 2 C0 3 , U0 2 (CO 3 ) 2 2 " and U0 2 (CO 3 ) 3 4-were identified. For the system uranyl-hydroxide the results were verified by analysis of conductance measurements. A similar investigation was carried out for thorium. Using Pu(IV)-chloride complexes as an example the potential of differential pulse voltarnmetry is demonstrated for the determination of small formation constants.

Plutonium / Voltammetry / Formation constants of plutonium chlorocomplexes / Radioactive waste disposal in salt diapirs SummaryThe formation constants of chlorocomplexes of Pu(IV) were determined in saturated NaCl solutions, by use of Differential Pulse Voltammetry (DPV) with a rotating disk electrode, for modelling safety aspects of radioactive waste repositories located in salt diapirs. The results obtained are: lg/T 0Xl =0.13±0.02; lg*ox2= -1.6s ±0.2; lg.K"3= -0.15±0.2. The special electrochemical equations necessary for describing the half-wave potential vs. chloride concentration and for applying a new iteration process were derived under the boundary conditions present. The equations and the complexing influence of hydrolysis are discussed in detail.