Antagonistic Role of Aqueous Complexation in the Solvent Extraction and Separation of Rare Earth Ions

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.

[1]  Masayuki Watanabe,et al.  Stoichiometry of Lanthanide-Phosphate Complexes at the Water Surface Studied Using Vibrational Sum Frequency Generation Spectroscopy and DFT Calculations. , 2021, The journal of physical chemistry. B.

[2]  A. Clark,et al.  Origins of Clustering of Metalate-Extractant Complexes in Liquid-Liquid Extraction. , 2020, ACS applied materials & interfaces.

[3]  H. Allen,et al.  Molecular Recognition and Hydration Energy Mismatch Combine To Inform Ion Binding Selectivity at Aqueous Interfaces. , 2020, The journal of physical chemistry. A.

[4]  H. Allen,et al.  Thermodynamic Signatures of the Origin of Anti-Hofmeister Selectivity for Phosphate at Aqueous Interfaces. , 2020, The journal of physical chemistry. A.

[5]  Kaitlin A. Lovering,et al.  Anions Enhance Rare Earth Adsorption at Negatively Charged Surfaces. , 2020, The journal of physical chemistry letters.

[6]  Lu-Yin Lin,et al.  Hydrogen-Bond Driven Chemical Separations: Elucidating the Interfacial Steps of Self-Assembly in Solvent Extraction. , 2020, ACS applied materials & interfaces.

[7]  Kaitlin A. Lovering,et al.  The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate , 2019, The Journal of Physical Chemistry C.

[8]  W. Bu,et al.  X-Ray Studies of Liquid Interfaces in Model Solvent Extraction Systems , 2019, Ion Exchange and Solvent Extraction: Volume 23.

[9]  H. Allen,et al.  Interfacial Supramolecular Structures of Amphiphilic Receptors Drive Aqueous Phosphate Recognition. , 2019, Journal of the American Chemical Society.

[10]  P. Dutta,et al.  Electrostatic Origin of Element Selectivity during Rare Earth Adsorption. , 2019, Physical review letters.

[11]  Thibault Cheisson,et al.  Rare earth elements: Mendeleev’s bane, modern marvels , 2019, Science.

[12]  W. Bu,et al.  Nanoscale view of assisted ion transport across the liquid–liquid interface , 2018, Proceedings of the National Academy of Sciences.

[13]  Masayuki Watanabe,et al.  The structure of a lanthanide complex at an extractant/water interface studied using heterodyne-detected vibrational sum frequency generation. , 2018, Physical chemistry chemical physics : PCCP.

[14]  A. Clark,et al.  Heavy Anionic Complex Creates a Unique Water Structure at a Soft Charged Interface , 2018, The Journal of Physical Chemistry C.

[15]  M. Antony,et al.  Effect of pKa on the extraction behavior of Am(III) in organo phosphorus acid and diglycolamide solvent system , 2018 .

[16]  B. Lin,et al.  Two-Step Adsorption of PtCl62– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations , 2017, 1709.04563.

[17]  Q. Xue,et al.  Selective recovery of rare earth elements from ion-adsorption rare earth element ores by stepwise extraction with HEH(EHP) and HDEHP , 2017 .

[18]  P. Dutta,et al.  Atomic Number Dependent "Structural Transitions" in Ordered Lanthanide Monolayers: Role of the Hydration Shell. , 2017, Langmuir : the ACS journal of surfaces and colloids.

[19]  E. Skovran,et al.  Lanthanide Chemistry: From Coordination in Chemical Complexes Shaping Our Technology to Coordination in Enzymes Shaping Bacterial Metabolism. , 2016, Inorganic chemistry.

[20]  L. Girard,et al.  Solvent Extraction: Structure of the Liquid-Liquid Interface Containing a Diamide Ligand. , 2016, Angewandte Chemie.

[21]  A. Gelis,et al.  High Precision Droplet-Based Microfluidic Determination of Americium(III) and Lanthanide(III) Solvent Extraction Separation Kinetics , 2016 .

[22]  Christina Kluge,et al.  Data Reduction And Error Analysis For The Physical Sciences , 2016 .

[23]  R. A. Campbell,et al.  Structure of a liquid/liquid interface during solvent extraction combining X-ray and neutron reflectivity measurements. , 2015, Physical chemistry chemical physics : PCCP.

[24]  Xiaowei Huang,et al.  Technology development for rare earth cleaner hydrometallurgy in China , 2015, Rare Metals.

[25]  S. Clarke,et al.  Neutron reflection study of the adsorption of the phosphate surfactant NaDEHP onto alumina from water. , 2015, Langmuir : the ACS journal of surfaces and colloids.

[26]  B. Lin,et al.  Observation of a rare earth ion-extractant complex arrested at the oil-water interface during solvent extraction. , 2014, The journal of physical chemistry. B.

[27]  D. Dreisinger,et al.  A critical review on solvent extraction of rare earths from aqueous solutions , 2014 .

[28]  D. Vaknin,et al.  Different Adsorption Behavior of Rare Earth and Metallic Ion Complexes on Langmuir Monolayers Probed by Sum-Frequency Generation Spectroscopy , 2013 .

[29]  P. Pershan,et al.  Liquid surfaces and interfaces : synchrotron X-ray methods , 2012 .

[30]  B. Lin,et al.  X-ray fluorescence from a model liquid/liquid solvent extraction system , 2011 .

[31]  A. Travesset,et al.  Ionic specificity in pH regulated charged interfaces: Fe3+ versus La3+. , 2011, Langmuir : the ACS journal of surfaces and colloids.

[32]  Liang Li,et al.  Toward mechanistic understanding of nuclear reprocessing chemistries by quantifying lanthanide solvent extraction kinetics via microfluidics with constant interfacial area and rapid mixing. , 2011, Journal of the American Chemical Society.

[33]  M. Nilsson,et al.  Review Article: A Review of the Development and Operational Characteristics of the TALSPEAK Process , 2007 .

[34]  F. Testard,et al.  Liquid–liquid extraction: An adsorption isotherm at divided interface? , 2007 .

[35]  P. J. Viccaro,et al.  The liquid surface/interface spectrometer at ChemMatCARS synchrotron facility at the Advanced Photon Source , 2003 .

[36]  P. Plieger,et al.  Metal Complexes for Hydrometallurgy and Extraction , 2003 .

[37]  K. Prochaska.  Interfacial activity of metal ion extractant. , 2002, Advances in colloid and interface science.

[38]  J. Szymanowski.  KINETICS AND INTERFACIAL PHENOMENA , 2000 .

[39]  P. J. Viccaro,et al.  A synchrotron x-ray liquid surface spectrometer , 1997 .

[40]  R. Heenan,et al.  Ammonium Bis(ethylhexyl) Phosphate: A New Surfactant for Microemulsions , 1996 .

[41]  Taichi Sato.  Liquid-liquid extraction of rare-earth elements from aqueous acid solutions by acid organophosphorus compounds , 1989 .

[42]  D. Dreisinger,et al.  THE KINETICS OF ZINC, COBALT AND NICKEL EXTRACTION IN THE D2EHPA-HEPTANE-HC104 SYSTEM USING THE ROTATING DIFFUSION CELL TECHNIQUE , 1989 .

[43]  V. Caron,et al.  United states. , 2018, Nursing standard (Royal College of Nursing (Great Britain) : 1987).

[44]  A. Gaonkar,et al.  Interfacial activity, extractant selectivity, and reversed micellization in hydrometallurgical liquid/liquid extraction systems , 1987 .

[45]  D. B. Drelsinger,et al.  THE KINETICS OF COBALT AND NICKEL EXTRACTION USING HEHEHP , 1986 .

[46]  M. A. Hughes,et al.  A general model to account for the liquid/liquid kinetics of extraction of metals by organic acids , 1984 .

[47]  Yizhak Marcus,et al.  Ionic radii in aqueous solutions , 1983 .

[48]  H. Freiser,et al.  Role of the interface in the extraction kinetics of zinc and nickel ions with alkyl-substituted dithizones , 1983 .

[49]  Y. Hasegawa,et al.  Solvent extraction chemistry : fundamentals and applications , 1977 .

[50]  H. Freiser,et al.  KINETICS OF EXTRACTION OF ZINC DITHIZONATE , 1962 .

[51]  D. F. Peppard,et al.  Fractional extraction of the lanthanides as their di-alkyl orthophosphates , 1957 .