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A novel macrocyclic calix[4]arene extractant having a long alkyl chain thioamide, 25,26,27,28-tetrakis( N - n -octylthiocarbamoyl)methoxy-5,11,17,23-tetra- tert -butylcalix[4]arene ( 1 ), was synthesized from 25,26,27,28-tetrakis( N - n -octylcarbamoyl)methoxy-5,11,17,23-tetra- tert -butylcalix[4]arene ( 2 ) using Lawesson’s reagent. Extractant  1  was characterized using  1 H NMR,  13 C NMR, FT-IR spectroscopy, and elemental analysis. The Pd(II) extraction abilities of  1  and  2  were studied in high-boiling-point and environmentally friendly hydrocarbon diluents. Pd(II) extraction experiments were conducted using single-metal Pd(II) solutions, simulated mixed palladium group metal (PGM) solutions, and acid-leached automotive catalyst residue solutions. Different experimental conditions, including the shaking time, HCl/HNO 3  concentration, Pd(II) concentration, extractant concentration, and the organic/aqueous phase ratio, were studied systematically. Extractant  1  showed very selective (> 99.9%) Pd(II) extraction from the mixed PGM/base metal solutions and the acid-leached automotive catalyst residue solution. Conversely, the Pd(II) extraction ability of extractant  2  was found to be negligible. Extractant  1  showed very fast extraction kinetics and a high extraction capacity as compared to those of the commercial extractant di- n -octyl sulfide. Effective stripping of Pd(II) from  1  was performed using HCI, HNO 3 , NH 3 , and HCl-thiourea solutions. Furthermore,  1  was successfully recycled over five extraction/stripping cycles. The Pd(II) extraction mechanism of  1  was studied using FT-IR spectroscopy. Extractant  1  exhibited very selective Pd(II) extraction and high acid stability, demonstrating its industrial applicability for the extraction of Pd(II) from leached automotive catalyst liquors containing PGMs and base metals.

scientific reports

Rapid and selective recovery of palladium from platinum group metals and base metals using a thioamide-modified calix[4]arene extractant in environmentally friendly hydrocarbon fluids