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

Abstract

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 1H NMR, 13C 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/HNO3 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, HNO3, NH3, 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.

The Elimination of Trace Arsenic Via Hollow Fiber Supported Liquid Membrane: Experiment and Mathematical Model

“…Eqs. (16) to (19), using the concept of Generating Function, as explained in Appendix A in Supplementary Information online, yields Eq.…”

“…Jantunen et al [13] separated arsenic from concentrated sulfuric acid using TBP (tributyl phosphate) as the extractant, extracting 83.7% of arsenic in threestages. As for the stripping of various metal ions, thiourea has been found to be effective [14][15][16].…”

Recovery of Palladium(II) and Platinum(IV) in Novel Extraction Systems

“…Hence, although many commercial extractants (e.g., Cyanex 923, TBP, Aliquat 336) have been proposed for PGM separation systems, still novel extraction systems are developed to improve the selectivity of PGM separation or decrease the number of extraction-stripping steps. Such novel extractants as piperidine-based [ 12 ], phosphonium or imidazolium quaternary salts (ionic liquids) [ 11 , 13 , 14 ], calixarenes [ 15 , 16 ], crown ethers [ 17 ] have been proposed to separate PGM, i.e., Pd(II), Pt(IV), Ru(III), or Rh(III) from aqueous acidic solutions.…”

The elimination of trace arsenic via hollow fiber supported liquid membrane: experiment and mathematical model

“…Jantunen et al 23 separated arsenic from concentrated sulfuric acid using TBP as the extractant attaining 83.7% of arsenic extracted in three-stages of separation. As for the stripping of various metal ions, thiourea has been found to be effective 24 – 26 . Fábrega and Mansur 27 found that thiourea could strip almost 100 percent of mercury(II) from mercury-Aliquat 336 complex.…”