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.
Using ultrasonic relaxation technique the kinetics of lanthanide nitrate complexation were investigated in the presence of excess nitrate ion for NdUII), Gd(III), Dy(II1) and Er(II1). The absorption spectra could most simply be interpreted in terms of a double relaxation. At 25°C the complexation rate constants, kS4, were 1.8 x lo8 s-' for Nd(II1) and 0.6 x los s-l for Er(1II). These rate constants were compared with those from earlier lanthanide complexation studies to interpret the overall complexation mechanism. Rate constants could not be obtained for the Dy and Gd systems.
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