SREL Reprint #3870

Age-dependent cementitious leachate effects on metal and radionuclide sorption to sediments from a subsurface waste-disposal site

Peng Lin1, Karah Greene1, Wei Xing1, Steven Simner2, Christina Logan2, Richard Henry2, and Daniel I. Kaplan1

1Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA
2Savannah River Mission Completion, Closure & Disposal Determinations, Aiken, SC, USA

Abstract: Risk assessment to evaluate long-term disposal for heavy metal and radioactive constituents at the subsurface engineered disposal facilities rely on distribution coefficients (Kd = Csolid/Cliquid). Low-level solid and liquid radioactive waste is disposed in the subsurface environment using various cementitious engineered barriers. This study measured Kd values to quantify the sorption–including adsorption, absorption, and/or precipitation for multiple metals/radionuclides in subsurface sediments impacted by cementitious leachates representing different cement aging stages, experimentally introduced as Cs(I), Sr(II), Ni(II), Eu(III), Th(IV), U(VI), Cr(VI), and Tc(VII), serving as chemical analogs of different chemical groups. Simulated groundwater (Stage IV) was used as a baseline besides three leachate simulants: freshly made concrete leachate (Stage I), portlandite (Stage II), and calcite (Stage III) to calculate the cementitious leachate impact factor (fCementLeach), defined as Kd-CementLeach/Kd-groundwater. Results showed significant changes in sorption between groundwater and leachate simulants. Monovalent cation analog Cs exhibited Kd values of 28–2390 L/kg (sandy) and 84–4230 L/kg (clayey), with fCementLeach up to 62 in sandy sediments impacted by young grout leachate. Divalent cations (Ni and Sr) and trivalent/tetravalent cations (Eu, Th) also showed strong enhancements in high-pH cementitious leachate environments; for example, Eu Kd increased from 25 L/kg in Stage IV groundwater to >67000 L/kg in leachates. Tetravalent cation analog Th showed very strong sorption (>10000 L/kg) in young and aged leachates, consistent with prior trivalent cation trends (Eu). Enhanced retention of multivalent cations (e.g., Ni2+, Eu3+, Th4+, and UO22+) in cementitious leachate-impacted sediments reflects not only surface sorption processes but also precipitation under elevated pH conditions, particularly in young grout leachate environments. Such precipitation-driven mechanisms were not evident for Cs+. Across cement aging stages, enhanced (Stage III) and/or reduced sorption (Stage II) can be observed for anionic species CrO42−, while 99TcO4−, a key risk driver, displayed minimal sorption and negligible response to cementitious leachates. These results represent the first extensive dataset quantifying cementitious leachate effects on sorption to sediments for different types of cation and anion metal contaminants. It also underscores how the evolution of cementitious barriers reshapes groundwater chemistry, directly influencing the predicted mobility of heavy metals and radionuclides in risk assessments.

Keywords: Distribution coefficients; Low-level waste; Performance assessment

SREL Reprint #3870

Lin, P., K. Greene, W. Xing, S. Simner, C. Logan, R. Henry, and D. I. Kaplan. 2026. Age-dependent cementitious leachate effects on metal and radionuclide sorption to sediments from a subsurface waste-disposal site. Applied Geochemistry 198(106701).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).