The Pu(IV)-Acetate Chemical Equilibria: Intrication between Hydrolysis and Complexation.

Area of Science:

• Radiochemistry
• Analytical Chemistry
• Solution Chemistry

Background:

• Previous studies suggested plutonium(IV) forms acetate complexes.
• The actual speciation of plutonium(IV) in aqueous solutions, particularly with ligands like acetate, remains complex and debated.

Purpose of the Study:

• To investigate the complexation of plutonium(IV) with acetate in aqueous solutions.
• To clarify the speciation of plutonium(IV) under acidic conditions using advanced analytical techniques.
• To challenge existing models of plutonium(IV) speciation in the presence of acetate.

Main Methods:

• Utilizing capillary electrophoresis (CE) coupled with inductively coupled plasma mass spectrometry (ICP-MS).
• Analyzing the plutonium(IV)/acetate/water system under acidic conditions (pH < 5.5).
• Determining equilibrium constants for hydrolysis and complexation kinetics.

Main Results:

• Plutonium(IV) acetate complexation, as previously described, does not exist under studied conditions.
• Two distinct coexisting kinetics, slow hydrolysis and fast complexation, were identified.
• Plutonium(IV) hydroxo complexes ([Pu(OH)y]4-y) form mixed complexes with acetate independently.
• Capillary electrophoresis successfully probed hydration spheres and size variations during complexation.

Conclusions:

• Existing literature data on plutonium(IV) speciation should be re-evaluated, focusing on hydroxo complexes rather than free Pu4+.
• Capillary electrophoresis provides valuable structural information about ions in solution, including hydration and complexation.
• This research offers new perspectives on understanding complex chemical systems beyond basic thermodynamics.