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

SCS pincer ligands 1 – 4 were synthesised, and their ability to extract Pd(II) from HCl and HNO 3 media was studied. The Pd(II) extraction properties of 1 – 4 were compared with those of commercial extractants (DOS and LIX ® 84-I) in kerosene. 1 and 2 showed superior Pd(II) extractability ( E % = 99.9) relative to DOS and LIX ® 84-I from 0.1–8.0 M HCl and to DOS from 0.1–8.0 M HNO 3 and mixed HCl + HNO 3 media. The Pd(II) extraction rate, acid durability, the most suitable organic/aqueous (O/A) phase ratio, and Pd(II) loading capacity of extractants 1 , 2 , and DOS were evaluated. 1 and 2 exhibited a greater Pd(II) extraction rate and Pd(II) loading capacity than DOS. 1 was very stable in acid media (HCl and HCl + HNO 3 ), whereas 2 and DOS deteriorated in HCl + HNO 3 . Selective extraction of Pd(II) by 1 and 2 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 1 and 2 were studied. The Pd(II) extraction mechanism of 1 – 4 was investigated using FT-IR, UV-visible, and NMR spectroscopy.