Synthesis of pincer-type extractants for selective extraction of palladium from PGMs: An improved liquid-liquid extraction approach to current refining processes


<jats:title>Abstract</jats:title><jats:p>SCS pincer ligands <jats:bold>1</jats:bold>–<jats:bold>4</jats:bold> were synthesised, and their ability to extract Pd(II) from HCl and HNO<jats:sub>3</jats:sub> media was studied. The Pd(II) extraction properties of <jats:bold>1</jats:bold>–<jats:bold>4</jats:bold> were compared with those of commercial extractants (DOS and LIX<jats:sup>®</jats:sup>84-I) in kerosene. <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> showed superior Pd(II) extractability (<jats:italic>E</jats:italic>% = 99.9) relative to DOS and LIX<jats:sup>®</jats:sup>84-I from 0.1–8.0 M HCl and to DOS from 0.1–8.0 M HNO<jats:sub>3</jats:sub> and mixed HCl + HNO<jats:sub>3</jats:sub> media. The Pd(II) extraction rate, acid durability, the most suitable organic/aqueous (O/A) phase ratio, and Pd(II) loading capacity of extractants <jats:bold>1</jats:bold>, <jats:bold>2</jats:bold>, and DOS were evaluated. <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> exhibited a greater Pd(II) extraction rate and Pd(II) loading capacity than DOS. <jats:bold>1</jats:bold> was very stable in acid media (HCl and HCl + HNO<jats:sub>3</jats:sub>), whereas <jats:bold>2</jats:bold> and DOS deteriorated in HCl + HNO<jats:sub>3</jats:sub>. Selective extraction of Pd(II) by <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> was achieved from a mixed solution containing Pd, Pt, Rh, rare metals, and base metal ions that simulated the leach liquors of automotive catalysts. The back extraction of Pd(II) and reusability of extractants <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> were studied. The Pd(II) extraction mechanism of <jats:bold>1</jats:bold>–<jats:bold>4</jats:bold> was investigated using FT-IR, UV-visible, and NMR spectroscopy.</jats:p>


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