CSE Colloquium Series

ARGONNE NATIONAL LABORATORY

CHEMICAL SCIENCES AND ENGINEERING DIVISION

 

SPEAKER:         Thomas Fanghänel

                             European Commission, JRC

                             Institute for Transuranium Elements

 

TITLE:                 Solubility and Redox Equilibria of Plutonium

 

TIME:                  11:00 am

     (Refreshments will be available starting at 10:45 am in front lobby)

 

DATE:                 March 3, 2008

 

PLACE:               Building 200, Auditorium

 

HOST:                 Lynn Soderholm/Paul Fenter         

 

Abstract:  The redox behavior of Pu, the hydrolysis of Pu(IV), and the solubility of Pu(IV) hydrous oxide in the presence of oxygen are discussed controversially in the literature. Experimental results are often discussed in terms of kinetic effects or radiolysis. Results of our recent study of the redox behavior of Pu(IV) solutions at low pH and of the solubility of Pu(IV) hydrous oxide at pH 2-12 (under Argon ant traces of oxygen) are presented. Pu-242 was used in order to avoid strong impact of radiolysis on the experimental results. While in many previous studies redox potentials were considered as not reliable or even not measured our results clearly indicate that the measured redox potentials can be discussed in terms of equilibrium thermodynamics and are a key parameter for the understanding of the aqueous Pu chemistry. With the known equilibrium constants summarized in the NEA-TDB for the system Pu/e^-/H⁺/OH^-/NaCl or NaClO₄/H₂O (25°C) and additional data determined for PuO_2+x(s,hyd) and small Pu(IV) colloids/polymers (1.5-2 nm) which are an integrated part of the thermodynamic system for the first time the total Pu solubility and oxidation state distribution is explained consistently in terms of equilibrium thermodynamics.