Abstract
Solvent extraction is used widely for chemical separations and environmental remediation. Although the kinetics and efficiency of this process rely upon the formation of ion-extractant complexes, it has proven challenging to identify the location of ion-extractant complexation within the solution and its impact on the separation. Here, we use tensiometry and X-ray scattering to characterize the surface of aqueous solutions of lanthanide chlorides and the water-soluble extractant bis(2-ethylhexyl) phosphoric acid (HDEHP), in the absence of a coexisting organic solvent. These studies restrict ion-extractant interactions to the aqueous phase and its liquid-vapor interface, allowing us to explore the consequences that one or the other is the location of ion-extractant complexation. Unexpectedly, we find that light lanthanides preferentially occupy the liquid-vapor interface. This contradicts our expectation that heavy lanthanides should have a higher interfacial density since they are preferentially extracted by HDEHP in solvent extraction processes. These results reveal the antagonistic role played by ion-extractant complexation within the aqueous phase and clarify the advantages of complexation at the interface. Extractants in common use are often soluble in water, in addition to their organic phase solubility, and similar effects to those described here are expected to be relevant to a variety of separations processes.
| Original language | English |
|---|---|
| Pages (from-to) | 1908-1918 |
| Number of pages | 11 |
| Journal | ACS Central Science |
| Volume | 7 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 24 2021 |
| Externally published | Yes |
Funding
This research is performed using funding received from the DOE Office of Nuclear Energy’s Nuclear Energy University Program under Award DE-NE0008779 to M.L.S., A.V.G., and M.A.B. This material is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences Separations Program under Award DE-SC0018200 to M.L.S. and I.B. NSF’s ChemMatCARS Sector 15 is funded by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under Grant NSF/CHE-1834750. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract DE-AC02-06CH11357. We thank Frederick Richard for assistance in measuring the X-ray data from pH 2.0 samples.
| Funders | Funder number |
|---|---|
| Materials Research | |
| National Science Foundation | NSF/CHE-1834750 |
| U.S. Department of Energy | DE-AC02-06CH11357 |
| Division of Materials Research | |
| Division of Chemistry | |
| Office of Science | DE-SC0018200 |
| Office of Nuclear Energy | DE-NE0008779 |
| Argonne National Laboratory |