Public Abstract

DE-FG02-07ER15880: Neptunyl and Uranyl Peroxide Chemistry in Molten Salts, Uranyl Structures from Nature, and Thermodynamic Studies Extending into the Transuranium Elements

Award Status: Inactive

Institution: University of Notre Dame du Lac, Notre Dame, IN
UEI: FPU6XGFXMBE9
DUNS: 824910376

Most Recent Award Date: 07/27/2021
Number of Support Periods: 14
PM: Wilk, Philip

Current Budget Period: 07/01/2020 - 06/30/2022
Current Project Period: 07/01/2019 - 06/30/2022
PI: Burns, Peter

Supplement Budget Period: N/A

Public Abstract

The chemistry of the actinides is extremely varied, complex, and fascinating, and in many respects actinide chemistry is a frontier research direction. Although uranyl peroxide compounds have been recognized since 1877, the amazing complexity of nanoscale uranyl peroxide cage clusters that form in water has only been revealed by us over the past 15 years. The interaction of peroxide with uranyl and neptunyl ions is very strong and favors complex clusters that are inherently nanoscale. We will explore a new direction in actinide peroxide chemistry by focusing on molten chloride (or fluoride) salts containing dissolved alkali peroxides with actinides. For example, lithium peroxide dissolves in a KCl-LiCl eutectic at 420 ºC and produces a peroxide rich solvent suitable for synthesis of novel actinide complexes and compounds. We will use differential scanning calorimetry to explore dissolution of alkali peroxides into various molten salt eutectics and the dissolution of different uranium and neptunium compounds therein and will crystalize novel actinide peroxides for structural, chemical, thermodynamic, and spectroscopic characterization. We will continue to turn to Nature to gain further insights into the complex structural chemistry of uranyl. In collaboration with mineralogists interested in new uranyl mineral species, we will study the structures and compositions of several new species and develop routes for their synthesis in some cases. In collaboration with scientists at Carnegie Institute, we will develop big data network analyses of uranium mineral chemical, structural, and occurrence relationships. Through a substantial University of Notre Dame investment, we have created a facility for measuring thermodynamic properties of actinide materials. This facility includes two drop-solution Calvert-type calorimeters with high temperature flux, two mixing calorimeters that operate from ambient to 300 ºC, and a differential scanning calorimeter. We propose to use these to collect thermodynamic data for a series of isostructural tetravalent actinide sulfate compounds extending from the lanthanides into the transuranium elements, as well as a suite of sodium uranyl sulfate minerals that provide an excellent opportunity to study relationships between structure stability and structural unit and interstitial complex charge densities. This will provide unique and powerful data for benchmarking computational methods in other groups, and such data is currently largely lacking. The specific scientific objectives of this proposal are: (1) Synthesis of actinide peroxide compounds in molten salt eutectics, (2) Studies of new uranyl minerals with fascinating structures and compositions, (3) Drop-solution calorimetric studies of actinide compounds extending into the transuranium elements, with an emphasis on the uranyl-sulfate system, (4) Continuation of studies of uranyl vanadate clusters synthesized using ionic liquids.

The chemistry of the actinides is extremely varied, complex, and fascinating, and in many respects actinide chemistry is a frontier research direction. Although uranyl peroxide compounds have been recognized since 1877, the amazing complexity of nanoscale uranyl peroxide cage clusters that form in water has only been revealed by us over the past 15 years. The interaction of peroxide with uranyl and neptunyl ions is very strong and favors complex clusters that are inherently nanoscale. We will explore a new direction in actinide peroxide chemistry by focusing on molten chloride (or fluoride) salts containing dissolved alkali peroxides with actinides. For example, lithium peroxide dissolves in a KCl-LiCl eutectic at 420 ºC and produces a peroxide rich solvent suitable for synthesis of novel actinide complexes and compounds. We will use differential scanning calorimetry to explore dissolution of alkali peroxides into various molten salt eutectics and the dissolution of different uranium and neptunium compounds therein and will crystalize novel actinide peroxides for structural, chemical, thermodynamic, and spectroscopic characterization. We will continue to turn to Nature to gain further insights into the complex structural chemistry of uranyl. In collaboration with mineralogists interested in new uranyl mineral species, we will study the structures and compositions of several new species and develop routes for their synthesis in some cases. In collaboration with scientists at Carnegie Institute, we will develop big data network analyses of uranium mineral chemical, structural, and occurrence relationships.

Through a substantial University of Notre Dame investment, we have created a facility for measuring thermodynamic properties of actinide materials. This facility includes two drop-solution Calvert-type calorimeters with high temperature flux, two mixing calorimeters that operate from ambient to 300 ºC, and a differential scanning calorimeter. We propose to use these to collect thermodynamic data for a series of isostructural tetravalent actinide sulfate compounds extending from the lanthanides into the transuranium elements, as well as a suite of sodium uranyl sulfate minerals that provide an excellent opportunity to study relationships between structure stability and structural unit and interstitial complex charge densities. This will provide unique and powerful data for benchmarking computational methods in other groups, and such data is currently largely lacking.

The specific scientific objectives of this proposal are: (1) Synthesis of actinide peroxide compounds in molten salt eutectics, (2) Studies of new uranyl minerals with fascinating structures and compositions, (3) Drop-solution calorimetric studies of actinide compounds extending into the transuranium elements, with an emphasis on the uranyl-sulfate system, (4) Continuation of studies of uranyl vanadate clusters synthesized using ionic liquids.