Selective extraction of Pd(II) ions from automotive catalyst residue in Cl− media by O-thiocarbamoyl-functionalized thiacalix[n]arenes

The extraction of Pd(II) ions from automotive catalyst residue solutions in Cl− media was studied using 5,11,17,23,29,35-tert-butyl-37,38,39,40,41,42-(dimethylthiocarbamoyl)oxy thiacalix[6]arene (1) and 5,11,17,23-tert-butyl-25,26,27,28-(dimethylthiocarbamoyl)oxy thiacalix[4]arene (2). Compounds 1 and 2 were found to have higher Pd(II)-ion extraction abilities than p-tert-butylthiacalix[6]arene (3) and p-tert-butylthiacalix[4]arene (4) in Cl− media. The prepared compounds selectively extracted Pd(II) ions from the single-metal, simulated mixed-metal, and automotive catalyst leached solutions. Compound 1 extracts 99.5–82% of Pd(II) from 0.1–2.0 M HCl media and 75–55% from 4.0–8.0 M HCl media. Compounds 1 and 2 have very high Pd(II)-loading capacities, which depend on the number of dimethylthiocarbamoyl moieties in 1 and 2. Pd(II) extraction efficiency of 1 and 2 was dependent on the Cl− concentration and independent of the H+ concentration. The acid durability test of the extractants was carried out with 2.0 M HCl–1.0 M HNO3 solutions. The FT-IR results showed that compounds 1 and 2 are more durable than compounds 3 and 4 in acidic media and are suitable for metal extraction in highly acidic media. In addition, compounds 1 and 2 selectively extracted 99% of Pd(II) ions from an automotive catalyst residue leached solution composed of Rh, Pd, Pt, Zr, Ce, Ba, Al, La, and Y in 1.0 M Cl− media. Thus, 1 and 2 can be used as effective extractants for Pd(II) separation from secondary resources.