Effects of Ionic Strength, Salt, and pH on Aggregation of Boehmite Nanocrystals: Tumbler Small-Angle Neutron and X-ray Scattering and Imaging Analysis

L. M. Anovitz, X. Zhang, J. Soltis, E. Nakouzi, A. J. Krzysko, J. Chun, G. K. Schenter, T. R. Graham, K. M. Rosso, J. J. De Yoreo, A. G. Stack, M. Bleuel, C. Gagnon, D. F.R. Mildner, J. Ilavsky, I. Kuzmenko

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28 Scopus citations

Abstract

The US government currently spends significant resources managing the legacies of the Cold War, including 300 million liters of highly radioactive wastes stored in hundreds of tanks at the Hanford (WA) and Savannah River (SC) sites. The materials in these tanks consist of highly radioactive slurries and sludges at very high pH and salt concentrations. The solid particles primarily consist of aluminum hydroxides and oxyhydroxides (gibbsite and boehmite), although many other materials are present. These form complex aggregates that dramatically affect the rheology of the solutions and, therefore, efforts to recover and treat these wastes. In this paper, we have used a combination of transmission and cryo-transmission electron microscopy, dynamic light scattering, and X-ray and neutron small and ultrasmall-angle scattering to study the aggregation of synthetic nanoboehmite particles at pH 9 (approximately the point of zero charge) and 12, and sodium nitrate and calcium nitrate concentrations up to 1 m. Although the initial particles form individual rhombohedral platelets, once placed in solution they quickly form well-bonded stacks, primary aggregates, up to ∼1500 Å long. These are more prevalent at pH = 12. Addition of calcium nitrate or sodium nitrate has a similar effect as lowering pH, but approximately 100 times less calcium than sodium is needed to observe this effect. These aggregates have fractal dimension between 2.5 and 2.6 that are relatively unaffected by salt concentration for calcium nitrate at high pH. Larger aggregates (>∼4000 Å) are also formed, but their size distributions are discrete rather than continuous. The fractal dimensions of these aggregates are strongly pH-dependent, but only become dependent on solute at high concentrations.

Original languageEnglish
Pages (from-to)15839-15853
Number of pages15
JournalLangmuir
Volume34
Issue number51
DOIs
StatePublished - Dec 26 2018

Funding

This research was supported by the Interfacial Dynamics in Radioactive Environments and Materials (IDREAM), an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES). This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. (U)SAXS data were collected at on beamline 9IC-D at the Advanced Photon Source, Argonne National Laboratory. We acknowledge the support of the National Institute of Standards and Technology, Center for Neutron Research, US Department of Commerce in providing the research neutron facilities used in this work. Access to both NBG30 SANS and BT5 USANS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under Agreement No. DMR-1508249. Certain commercial equipment, instruments, materials, and software are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology or the Department of Energy nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. The authors have no pertinent commercial of other relationships that are known to them to create a conflict of interest. A portion of this research was performed using EMSL, a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research and located at PNNL. PNNL is a multiprogram national laboratory operated for DOE by Battelle Memorial Institute under Contract No. DE-AC06-76RLO-1830. We would also like to thank Xiaohong Shari Li (PNNL) for the BET measurements.

FundersFunder number
DOE Office of Biological and Environmental Research
DOE Office of Science
IDREAM
Interfacial Dynamics in Radioactive Environments and Materials
National Institute of Standards and Technology, Center for Neutron Research
US Department of Energy
National Science Foundation
U.S. Department of Energy
National Institute of Standards and Technology
U.S. Department of Commerce
Battelle
Office of Science
Basic Energy Sciences
Argonne National Laboratory
Pacific Northwest National Laboratory

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