Assessment of the Thermodynamic Behaviour of Neptunium in Water and Model Groundwaters from 25 to 150 Degrees C

摘要

Standard molal Gibbs energy of formation and entropy data for simple neptunium solids and aqueous neptunium complexes with OH exp - , Cl exp - , F exp - , CO sub 32- , PO sub 43- , SO-4 exp 2- and Na exp + have been critically reviewed. Selected values are used with estimated heat capacity values to derive self-consistent analytical expressions for the temperature dependence of the standard molal Gibbs energies of formation of the species from 25 to 150 degrees C. The Gibbs energies have been used to evaluate the effect of different concentrations of ligands on the solubility of neptunium solids as a function of temperature. Potential-pH diagrams are given for neptunium in pure water and in two model groundwaters. Important deficiencies in the available thermodynamic data for neptunium species are discussed. (Atomindex citation 16:041385)