Proton Chelating Ligands Drive Improved Chemical Separations for Rhodium

Hirokazu Narita, Rebecca M. Nicolson, Ryuhei Motokawa, Fumiyuki Ito, Kazuko Morisaku, Midori Goto, Mikiya Tanaka, William T. Heller, Hideaki Shiwaku, Tsuyoshi Yaita, Ross J. Gordon, Jason B. Love, Peter A. Tasker, Emma R. Schofield, Mark R. Antonio, Carole A. Morrison

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

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 these processes, particularly in the hydrometallurgical separation step. While many of the precious metals can be separated by solvent extraction, there currently exist no commercial extraction reagents 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-hexyl-bis(N-methyl-N-n-octyl-ethylamide)amine transports Rh(III) from aqueous HCl into an organic phase as the mono-aquated 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, ESI-MS) and computational modeling. The paper demonstrates the importance of applying a broad range of techniques to obtain a convincing mode of action view 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 rational design of the next generation 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.
Original languageEnglish
Pages (from-to)8720-8734
Number of pages15
JournalInorganic Chemistry
Issue number13
Early online date17 Jun 2019
Publication statusPublished - 1 Jul 2019

Keywords / Materials (for Non-textual outputs)

  • HCL


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