Rate of radiocarbon retention onto calcite by isotope exchange
-
Janne Lempinen
and
Jukka Lehto
Abstract
Radiocarbon (14C) is a top priority class radionuclide associated with the long-term safety of spent nuclear fuel disposal. Dissolved inorganic radiocarbon can be retained in bedrock via isotope exchange with calcite (CaCO3) at solubility equilibrium with groundwater. In the present study, the rate of the isotope exchange process was investigated on synthetic calcite using batch experiments. Experiments were performed in solutions with a calcium concentration of 0.0002–0.1 M, including two synthetic reference groundwaters. The radiocarbon activity in the solutions decreased exponentially as a function of time, thus following first-order kinetics. The rate of isotope exchange was quantified from an exponential fit to the activity data over time. The rate of radiocarbon retention increased as a function of the calcium activity. The isotope exchange half-life was only 4.3 days at calcium ion activities over 0.01. This half-life is very much shorter than the half-life of 14C or the time scale of groundwater movements; consequently calcite can effectively retain radiocarbon from brackish and saline groundwaters.
Acknowledgement
This study has received funding from the Finnish Research Programme on Nuclear Waste Management (KYT-2014, KYT-2018). The authors are also grateful to Mr. Dennis Apter and Ms. Shenelle Ghulam at the University of Helsinki for performing some of the measurements and to Dr. Stellan Holgersson at Chalmers Tehnical University for the BET measurement
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Articles in the same Issue
- Frontmatter
- Uses of alpha particles, especially in nuclear reaction studies and medical radionuclide production
- Direct flow separation strategy, to isolate no-carrier-added 90Nb from irradiated Mo or Zr targets
- Sorption of Th(IV) onto ZnO nanoparticles and diatomite-supported ZnO nanocomposite: kinetics, mechanism and activation parameters
- The influence of pH and reaction time on the formation of FeSe2 upon selenite reduction by nano-sized pyrite-greigite
- Chitosan-ferrocyanide sorbent for Cs-137 removal from mineralized alkaline media
- Rate of radiocarbon retention onto calcite by isotope exchange
- Evaluation of excess life time cancer risk due to natural radioactivity of the Lignite samples of the Nichahoma, lignite belt, North Kashmir, India
