Proton Chelating Ligands Drive Improved Chemical Separations for Rhodium
Proton Chelating Ligands Drive Improved Chemical Separations for Rhodium
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DOI：
10.1021/acs.inorgchem.9b01136
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发表时间：
2019-07-01
影响因子：
4.6
通讯作者：
Morrison, Carole A.
中科院分区：
文献类型：
--
作者：
Narita, Hirokazu;Nicolson, Rebecca M.;Morrison, Carole A.
在现代技术应用中使用的所有元素中，目前的铑提取方法的碳足迹最高，污染指标最严重。由于对萃取过程，特别是湿法冶金分离步骤中发生的分子水平化学的了解有限，对现有方法的改进变得困难。虽然许多贵金属可以通过溶剂萃取分离，但目前还没有用于Rh的商业萃取剂。这是由于它在浸出到盐酸中时形成复杂的混合形态，这给设计有效的溶剂萃取试剂带来了困难。本研究表明，二胺试剂n- n-己基双（n-甲基-n- n-辛基乙胺）胺通过形成外球组装体将Rh（III）从水溶液中的HCl转运为一水离子[RhCl5(H2O)](2-)；通过实验（坡度分析，FT-IR和NMR光谱，EXAFS， SANS和ESI-MS）和计算建模对该组合进行了表征。本文论证了应用广泛的技术来获得在溶液阶段阴离子识别中涉及的复杂过程的令人信服的作用模式的重要性。一个一致的和全面的理解配体是如何实现相对于竞争对手阴离子Cl-的Rh（III）选择性的。这些知识将指导萃取剂的设计，从而为提高从传统采矿来源和二次来源材料的回收中提取金属的可持续性提供了希望。
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.