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Abstract
Small‐angle neutron scattering (SANS) data for n‐octane solutions of TBP loaded with progressively larger amounts of HNO3, HClO4, H2SO4, and H3PO4 up to and beyond the LOC (limiting organic concentration of acid) condition, were interpreted using the Baxter model for hard spheres with surface adhesion. The coherent picture of the behavior of the TBP solutions derived from the SANS investigation discussed in this paper confirmed our recently developed model for third phase formation. This model analyses the features of the scattering data in the low Q region as arising from van der Waals interactions between the polar cores of reverse micelles. Our SANS data indicated that the TBP micelles swell when acid and water are extracted into their polar core. The swollen micelles have critical diameters ranging from 15 to 22 Å, and polar core diameters between 10 and 15 Å, depending on the specific system. At the respective LOC conditions, the TBP weight‐average aggregation numbers are ∼4 for HClO4, ∼6 for H2SO4, ∼7 for HCl, and ∼10 for H3PO4. The comparison between the behavior of HNO3, a non‐third phase forming acid, and the other acids provided an explanation of the effect of the water molecules present in the polar core of the micelles on third phase formation. The thickness of the lipophilic shell of the micelles indicated that the butyl groups of TBP lie at an angle of ∼25 degrees relative to a plane tangent to the micellar core. The critical energy of intermicellar attraction, U(r), was about −2 kBT for all the acids investigated. This value is the same as that reported in our previous publications on the extraction of metal nitrates by TBP, confirming that the same mechanism and energetics are operative in the formation of a third phase, independent of whether the chemical species extracted are metal nitrate salts or inorganic acids.
The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy, Office of Science laboratory, is operated under Contract No. DE‐AC02‐06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
ACKNOWLEDGMENTS
We thank Denis Wozniak (IPNS) for help provided during the SANS measurements. This work was supported by the U. S. Department of Energy, Office of Basic Energy Science, Division of Chemical Sciences, Biosciences, and Geosciences (for the part performed at the Chemistry Division of ANL) and Division of Material Science (for the part performed at INPS), under contract No. DE‐AC02‐06CH11357.
The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W‐31‐109‐ENG‐38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
Notes
The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy, Office of Science laboratory, is operated under Contract No. DE‐AC02‐06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
