Abstract
Successful deployment of in situ subsurface remediation strategies requires knowledge of contaminant geochemistry, and the impact of physicochemical sediment properties on remedy performance. Bismuth (Bi) materials can sequester multiple contaminants that are present in the unsaturated zone and groundwater at Department of Energy (DOE) legacy nuclear sites, such as the Hanford Site. Adsorption experiments for individual contaminants (chromate, iodate, pertechnetate, and uranyl carbonate) were conducted with two Bi materials: commercially available Bi-subnitrate (BSN); and laboratory synthesized Bi oxyhydroxide nitrate (BOH). The structure and composition of the Bi material influenced hydrolysis and ion exchange interactions in aqueous solution, with subsequent impacts on solution pH, contaminant speciation, and contaminant uptake. X-ray diffraction revealed that the disordered BOH structure, initially containing charge balancing nitrate and hydroxide anions, rapidly converted to bismutite, Bi2O2(CO3), in the presence of carbonate. During this transformation, BOH removed most contaminant ions from solution. [Bi6O5(OH)3]5+ clusters in BSN underwent hydrolysis upon exposure to aqueous solutions, substantially reducing pH, and transforming into several mineral phases, including a daubreeite (BiO(OH,Cl)) structure, and an unidentified mineral phase (unk-Bi(NO3)x(OH)yOz). This transformation decreased uptake efficiency relative to BOH, except for pertechnetate. The adsorption isotherms for the contaminants were fit with a Freundlich model that describes adsorption to Bi materials with dissimilar binding sites. Solid phase characterization after reaction confirmed structural rearrangement of the Bi materials and direct association of the contaminant ions with Bi mineral structures via different mechanisms, including anion exchange or outer-sphere complexation for pertechnetate, and inner-sphere adsorption for all other contaminants. Uranyl carbonate could substitute between the [Bi2O2]2+ layers, and some iodate was incorporated into a neo-formed δ-Bi2O3 phase. This remarkable versatility of Bi-based materials demonstrated here means that they are cost-effective materials with the potential to sequester co-located contaminants at DOE legacy sites.
| Original language | English |
|---|---|
| Pages (from-to) | 17350-17375 |
| Number of pages | 26 |
| Journal | Journal of Materials Chemistry A |
| Volume | 13 |
| Issue number | 23 |
| DOIs | |
| State | Published - Apr 23 2025 |
Funding
This document was prepared by the Deep Vadose Zone - Applied Field Research Initiative at Pacific Northwest National Laboratory. Funding for this work was provided by the U.S. Department of Energy (DOE) Hanford Field Office. The Pacific Northwest National Laboratory (PNNL) is operated by Battelle Memorial Institute for the DOE under Contract DE-AC05-76RL01830. Solid phase characterization including XRD interpretation and SEM/EDS were performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at PNNL. Use of the Advanced Photon Source, an Office of Science User Facility operated by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. John Fulton is kindly acknowledged for providing the XANES and EXAFS data for CrO42− in solution. The authors greatly appreciate the technical review provided by Mike Truex and Chris Johnson and technical editing provided by Matt Wilburn. The authors would like to thank those who analyzed samples, reviewed data, and helped with experimental equipment, including Keith Geiszler, Steven Baum, Ian Leavy, Megan Nims, Michelle Valenta Snyder, and Ben Williams. This document was prepared by the Deep Vadose Zone – Applied Field Research Initiative at Pacific Northwest National Laboratory. Funding for this work was provided by the U.S. Department of Energy (DOE) Hanford Field Office. The Pacific Northwest National Laboratory (PNNL) is operated by Battelle Memorial Institute for the DOE under Contract DE-AC05-76RL01830. Solid phase characterization including XRD interpretation and SEM/EDS were performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at PNNL. Use of the Advanced Photon Source, an Office of Science User Facility operated by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. John Fulton is kindly acknowledged for providing the XANES and EXAFS data for CrO in solution. The authors greatly appreciate the technical review provided by Mike Truex and Chris Johnson and technical editing provided by Matt Wilburn. The authors would like to thank those who analyzed samples, reviewed data, and helped with experimental equipment, including Keith Geiszler, Steven Baum, Ian Leavy, Megan Nims, Michelle Valenta Snyder, and Ben Williams. 4