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Proton chelating ligands drive improved chemical separations for rhodium

DOI: 10.1021/acs.inorgchem.9b01136 DOI Help

Authors: Hirokazu Narita (National Institute of Advanced Industrial Science and Technology (AIST)) , Rebecca M. Nicolson (University of Edinburgh) , Ryuhei Motokawa (Japan Atomic Energy Agency (JAEA)) , Fumiyuki Ito (National Institute of Advanced Industrial Science and Technology (AIST)) , Kazuko Morisaku (National Institute of Advanced Industrial Science and Technology (AIST)) , Midori Goto (National Institute of Advanced Industrial Science and Technology (AIST)) , Mikiya Tanaka (National Institute of Advanced Industrial Science and Technology (AIST)) , William T. Heller (Oak Ridge National Laboratory) , Hideaki Shiwaku (Japan Atomic Energy Agency (JAEA)) , Tsuyoshi Yaita (Japan Atomic Energy Agency (JAEA)) , Ross J. Gordon (Johnson Matthey Technology Centre) , Jason B. Love (University of Edinburgh) , Peter A. Tasker (University of Edinburgh) , Emma R. Schofield (Johnson Matthey Technology Centre) , Mark R. Antonio (Argonne National Laboratory) , Carole A. Morrison (University of Edinburgh)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: June 2019
Diamond Proposal Number(s): 15757

Abstract: Current methods for the extraction of rhodium carry the highest carbon footprint and worst pollution metrics of all of the elements used in modern technological applications. Improving upon existing methods is made difficult by the limited understanding of the molecular-level chemistry occurring in extraction processes, particularly in the hydrometallurgical separation step. While many of the precious metals can be separated by solvent extraction, there currently exist no commercial extractants for Rh. This is due to its complicated mixed speciation upon leaching into hydrochloric acid, which gives rise to difficulties in designing effective reagents for solvent extraction. Herein we show that the diamidoamine reagent N-n-hexylbis(N-methyl-N-n-octylethylamide)amine transports Rh(III) from aqueous HCl into an organic phase as the monoaquated dianion [RhCl5(H2O)]2– through the formation of an outer-sphere assembly; this assembly has been characterized by experimentation (slope analysis, FT-IR and NMR spectroscopy, EXAFS, SANS, and ESI-MS) and computational modeling. The paper demonstrates the importance of applying a broad range of techniques to obtain a convincing mode of action for the complex processes involved in anion recognition in the solution phase. A consistent and comprehensive understanding of how the ligand operates to achieve Rh(III) selectivity over the competitor anion Cl– has emerged. This knowledge will guide the design of extractants and thus offers promise for improving the sustainability of metal extraction from both traditional mining sources and the recycling of secondary source materials.

Subject Areas: Chemistry, Environment


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