Plutonium oxidation and subsequent reduction by Mn(IV) minerals in Yucca Mountain tuff.
Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).
Powell
Brian A
BA
Department of Environmental Engineering and Science, Clemson University, Anderson, South Carolina 29630, USA. powell37@llnl.gov
Duff
Martine C
MC
Kaplan
Daniel I
DI
Fjeld
Robert A
RA
Newville
Matthew
M
Hunter
Douglas B
DB
Bertsch
Paul M
PM
Coates
John T
JT
Eng
Peter
P
Rivers
Mark L
ML
Serkiz
Steven M
SM
Sutton
Stephen R
SR
Triay
Ines R
IR
Vaniman
David T
DT
D006863:Hydrogen-Ion Concentration; D017895:Manganese Compounds / Q000032:analysis* / Q000737:chemistry; D008903:Minerals / Q000032:analysis* / Q000737:chemistry; D009505:Nevada; D010084:Oxidation-Reduction; D010087:Oxides / Q000032:analysis* / Q000737:chemistry; D011005:Plutonium / Q000032:analysis* / Q000737:chemistry; D011850:Radioactive Waste / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis; D013057:Spectrum Analysis / Q000379:methods; D013997:Time Factors
D017895:Manganese Compounds; D008903:Minerals; D010087:Oxides; D011850:Radioactive Waste; D012989:Soil Pollutants; D011005:Plutonium; C016552:manganese dioxide