TY - JOUR
T1 - A combined x-ray absorption and Mössbauer spectroscopy study on Fe valence and secondary mineralogy in granitoid fracture networks
T2 - Implications for geological disposal of spent nuclear fuels
AU - Yu, Changxun
AU - Drake, Henrik
AU - Dideriksen, Knud
AU - Tillberg, Mikael
AU - Song, Zhaoliang
AU - Mørup, Steen
AU - Åström, Mats E.
N1 - Funding Information:
The Swedish Nuclear Fuel and Waste Management Company (SKB) is gratefully acknowledged for financial support and providing access to samples/data. The XAS measurements were conducted at beamline I811, MAX-lab, Lund, Sweden. Dr. Stefan Carlson and Dr. Kajsa Sigfridsson at the beamline are thanked for their strong support during the XAS measurements. We kindly acknowledge Cathrine Frandsen for access to Mössbauer spectrometers and Helge K. Rasmussen for analyses. H.D. is thankful for a Swedish Research Council grant (Contract 2017-05186) and Formas grant (Contract 2017-00766).
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/3/3
Y1 - 2020/3/3
N2 - Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.
AB - Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.
UR - http://www.scopus.com/inward/record.url?scp=85080926294&partnerID=8YFLogxK
U2 - 10.1021/acs.est.9b07064
DO - 10.1021/acs.est.9b07064
M3 - Article
C2 - 32019302
AN - SCOPUS:85080926294
SN - 0013-936X
VL - 54
SP - 2832
EP - 2842
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 5
ER -