Selective sorption of palladium by thiocarbamoyl-substituted thiacalix[n]arene derivatives immobilized on amberlite resin: application to leach liquors of automotive catalysts†
p-tert-Butylthiacalix[4/6]arenes (1 and 2) and their thiocarbamoyl derivatives (3 and 4) were immobilized on Amberlite XAD-7 (XAD). Pd(II) adsorption from single-metal solution, simulated mixed-metal solution, and automotive catalyst leach liquor in HCl media was performed in the batch mode. The Pd(II) sorption capacity of 3 and/or 4 immobilized on XAD (7 and 8) was 40.2 mg g−1 and 60.0 mg g−1, respectively. In contrast, 1 and/or 2 immobilized on XAD (5 and 4) had lower sorption capacities than 7 and 8, 10.1 mg g−1 and 13.4 mg g−1, respectively. Resins 7 and 8 selectively sorbed 99% of Pd(II) ions from automotive catalyst liquor comprising Rh, Pd, Pt, Zr, Ce, Ba, Al, La, and Y in 0.1 M HCl media. XAD and the extractant-impregnated XAD resins were characterized by FT-IR, XRD, SEM-EDAX, and WDXRF before and after Pd(II) sorption. The sorption data were fitted to Freundlich and Langmuir isotherms. Thermodynamic parameters such as ΔGo, ΔHo, and ΔSo were calculated to evaluate the nature of the sorption process. The Pd(II) sorption efficiency of 7 and 8 was also tested by column method. Desorption of Pd(II) ions from the loaded resins was performed using acidic thiourea, thereby enabling recycling of the resins. Thus, both resins 7 and 8 can be used for the effective separation of Pd(II) from secondary resources.