Calix[4]arene-Based Amino Extractants Containing n-Alkyl Moieties for Separation of Pd(II) and Pt(IV) from Leach Liquors of Automotive Catalysts

Abstract

Pt, Pd, and Rh platinum group metals (PGMs) are utilized in automotive catalytic converters to reduce the level of harmful gas emissions. To evaluate the separation efficiencies of PGMs from the leach liquors of automotive catalysts, their extractabilities from both single-component solutions and leach liquors were determined using three p-dialkylaminomethylcalix[4]arenes (alkyl: n-hexyl~n-octyl; 3-5) as extractants, and the obtained results were compared with the data of acyclic p-din -octylaminomethyldimethylphenol (6) and those previously reported for macrocyclic calix[4]arene-and thiacalix[n]arene-based amine and amide extractants. Various extraction parameters, including the contact time, HCl concentration, and concentrations of Pd(II) and Pt(IV) ions, were examined, and the distributions and stoichiometry ratios of the recovered Pd(II) and Pt(IV) species were calculated. All macrocyclic extractants 3-5 exhibited high and selective extractabilities of Pd(II) and Pt(IV) ions contained in the leach liquors of automotive catalysts. The E% values of 3-5 from the leach liquors were 94.2, 93.0, and 97.7 for Pd(II) and 91.7, 94.0, and 92.5 for Pt(IV), respectively. Acyclic compound 6 did not perform well even though higher ratios of extractant used. Furthermore, the results of reusability testing demonstrated relatively large extractability values obtained for these two metals even after five extraction/stripping cycles.

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

“…The effect of HCl and HNO 3 concentration on Pd(II) extraction was performed using 0.1–8.0 M HCl or HNO 3 using 1 mM 1 and 2 in kerosene containing 20% n -octanol for 30 min. The distribution ratio ( D ) of Pd(II) with 1 was calculated using slope analysis 18 , 19 . The slope analysis was performed using 0.01–0.1 mM 1 with 1.0 mM Pd(II) in 0.1 M HCl.…”

“…Calix[4]arenes are readily synthesized by a facile one-pot procedure involving the condensation of HCHO with phenol 16 , 17 . Calix[4]arenes can be tailored to selectively bind specific PGMs using chemical modifications 18 , 19 . Thus, functionalized macrocyclic calix[4]arenes (basket-like molecules) can simplify the enrichment of PGMs and significantly decrease the use of excess extractants 20 .…”

“…Thus, functionalized macrocyclic calix[4]arenes (basket-like molecules) can simplify the enrichment of PGMs and significantly decrease the use of excess extractants 20 . Our previous results showed that macrocyclic calixarene or thiacalixarene-based extractants and other new thiocarbamoyl-based extractants are more durable in acid media than commercial extractants and extract approximately 3–5-fold more metal ions than commercial extractants from secondary resource leach liquors 19 , 21 – 28 . Generally, calixarenes and their derivatives are highly soluble only in aromatic/chlorinated diluents such as chloroform, dichloromethane, dichloroethane, and toluene 29 .…”

“…Generally, calixarenes and their derivatives are highly soluble only in aromatic/chlorinated diluents such as chloroform, dichloromethane, dichloroethane, and toluene 29 . To date, experiments on the PGM extraction capabilities of calixarene derivatives have only been conducted in chlorinated diluents 19 , 20 , 29 . However, the use of chlorinated diluents has several disadvantages, including their low boiling points and issues related to environmental and health concerns during industrial operations.…”

Chelating Extractants for Metals

“…From a technological point of view, it is not very convenient as it is very volatile, toxic and can react with silver salts. High extraction ability with respect to Pd (II) and Pt (IV) ions was found during the extraction of metals from leaching solutions of car catalysts in dialkylaminomethylcalix [4]arenes 92, 93 and 94 dissolved in saturated hydrocarbons [94,95].…”