SREL Reprint #3819

Uptake of technetium and iodine (I-, IO3- and organo-I) by pecan biochar

Peng Lin1, Brennan Ferguson1,2, Karah M. Greene1, Wei Xing1, Chen Xu3, Christopher E. Bagwell4,
Donald W. Watts5, and Daniel I. Kaplan1

1Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA
2Department of Geology, University of Georgia, Athens, GA, USA
3Laboratory for Environmental and Oceanographic Research, Department of Marine Sciences,
Texas A&M University-Galveston, Galveston, TX, USA
4Pacific Northwest National Laboratory, Earth Systems Science Division, Richland, WA, USA
5United States Department of Agriculture, Agricultural Research Service,
Coastal Plains Research Laboratory, Florence, SC, USA

Abstract: Remediation of land and groundwater that are contaminated with high-risk driving anionic-radionuclides, such as iodine-129 (I-129) and technetium-99 (Tc-99), remains an intractable problem. The objective of this study was to evaluate biochar materials as a low-cost and effective sorbent for Tc-99 and three iodine species, iodide/iodate/organo-iodine (org-I). Sorption studies were conducted with biochar derived from pecan shells (Carya illinoinensis), that underwent two pyrolysis temperatures (500°C and 700°C) and two types of acid-activation (H3PO4 and HCl). Acid-activated biochar had much higher sorption capacities (in terms of distribution coefficient, Kd, the concentration ratio of solid:liquid) for Tc-99 and different iodine species, than non-acid-activated biochar. The H3PO4-activated biochar (500°C) was the most effective sorbent with Tc-99 Kd of 49,390 ± 14,268 mL/g, iodide Kd of 2433 ± 312 mL/g, iodate Kd of 410 ± 168 mL/g, and org-I Kd of 857 ± 181 mL/g. The HCl-activated biochar (700°C) was also effective at sequestering Tc-99 (Kd of 7864 ± 5,585 mL/g) and iodide (Kd of 2481 ± 237 mL/g) but not for iodate/org-I. Solid-state 13C-nuclear magnetic resonance (NMR) analysis suggested the strong sorption capacity related to the formation of abundant alkene, aromatic and heteroaromatic functional groups, which was also supported by the Fourier-transform infrared spectroscopy (FTIR) analysis. Additionally, the FTIR suggested the possible electrophilic substitution of C-H by iodine to form C-I bond. Surface area measurements and SEM images indicated the H3PO4-activated biochar (500°C) had especially high surfaces areas. Functionalized biochar may provide a cost effective and efficient sorbent for sequestering I-129 and Tc-99 from the biosphere, thereby reducing human risk.

Keywords: Pecan biochar; Radionuclide; Kd; Environmental remediation; Biochar functionalization

SREL Reprint #3819

Lin, P., B. Ferguson, K. M. Greene, W. Xing, C. Xu, C. E. Bagwell, D. W. Watts, and D. I. Kaplan. 2025. Uptake of technetium and iodine (I-, IO3- and organo-I) by pecan biochar. Journal of Environmental Radioactivity 285(107674).

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