SREL Reprint #3711

Presence of aromatic-rich organic matter and its characterization in grout materials: Implications for radionuclide immobilization

Peng Lin1,2, Chen Xu2, Daniel I. Kaplan1, Chris M. Yeager3, Wei Xing1,2, Ralph Nichols4,
and Peter H. Santschi2

1Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, 29802, USA
2Department of Marine and Coastal Environmental Science, Texas A & M University Galveston Campus,
Galveston, TX, 77553, USA
3Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
4Savannah River National Laboratory, Aiken, SC, 29808, USA

Abstract: Grout materials are commonly used to immobilize low-level radioactive waste. Organic moieties can be unintentionally present in common ingredients used to make these grout waste forms, which may result in the formation of organo-radionuclide species. These species can positively or negatively affect the immobilization efficiency. However, the presence of organic carbon compounds is rarely considered in models or characterized chemically. Here, we quantify the organic pool of grout formulations with and without slag, as well as the individual dry ingredients used to make the grout samples (ordinary Portland cement (OPC), slag and fly ash), including total organic carbon (TOC) and black carbon, followed by aromaticity evaluation and molecular characterization via Electro Spray Ionization Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FTICRMS). All dry grout ingredients contained significant amounts of organic carbon, ranging from 550 mg/kg to 6250 mg/kg for the TOC pool, with an averaged abundance of 2933 ± 2537 mg/kg, of which 60 ± 29% was composed of black carbon. The significant abundance of a black carbon pool implies the presence of the aromatic-like compounds, which was further identified by both phosphate buffer-assisted aromaticity evaluation (e.g., >1000 mg-C/kg as aromatic-like carbon in the OPC) and dichloromethane (DCM) extraction with ESIFTICRMS analysis. Besides aromatic-like compounds, other organic moieties were also detected in the OPC, such as carboxyl-containing aliphatic molecules. While the organic compound only consists of minor fractions of the grout materials investigated, our observations of the presence of various radionuclide-binding organic moieties suggests the potential formation of organo-radionuclides, such as radioiodine, which might be present at lower molar concentrations than TOC. Evaluating the role of organic carbon complexation in controlling the disposed radionuclides, especially for those radionuclides with strong association with organic carbon, has important implications for the long-term immobilization of radioactive waste in grout systems.

Keywords: Cement, Fly ash, Iodine, ESI-FTICR-MS, Aromaticity, Black carbon

SREL Reprint #3711

Lin, P., C. Xu, D. I. Kaplan, C. M. Yeager, W. Xing, R. Nichols, and P. H. Santschi. 2023. Presence of aromatic-rich organic matter and its characterization in grout materials: Implications for radionuclide immobilization. Journal of Environmental Radioactivity 263.

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