One of Professor Nitsche’s many research areas was in the field of environmental actinide chemistry. In this presentation, studies of the redox specaition of Pu and other actinides at solid:water interfaces will be discussed in terms of the contributions of Professor Nitsche’s group and data generated by other reserachers. General observations are that regardless of the mineral composition, Pu(IV) was the predominant solid phase oxidation state at the end of each experiment. The stability of Pu(IV), even on oxidizing surfaces such as pyrolusite, is proposed to be due to formation of an energetically favorable solid phase Pu(IV) species. A series of X-ray Absorption Spectroscopy (XAS) experiments independently verified Pu(IV) as the stable oxidation state of Pu sorbed to a suite of mineral colloids including pyrolusite, birnessite, magnanite, hausmaniite, hematite, and goethite. Interestingly, independent XAS studies by Professor Nitsche’s group predicted similar distributions of Pu(IV), Pu(V), and Pu(VI) on the manganese oxide minerals hausmannite and manganite despite a five order of magnitude difference in Pu concentrations in the systems. The observations made from this work have helped to explain the observed mobility of Pu in a series of long term (11 year) field lysimeter experiments at the Savannah River Site. The lysimeter studies indicate that Pu transport can be described as a dynamic system where adsorption and surface mediated reduction of Pu(V/VI) appears to compete with a slow (possibly oxidative) release of Pu. These results demonstrate how field and laboratory studies can be combined to describe Pu behavior in complex environmental systems and highlight the need for a fundamental understanding of actinide environmental chemistry.

Heino Nitsche’s contributions to the understanding of Pu reactions at mineral:water interfaces and their implications on present reactive transport modeling

249th National Meeting (2015)

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