Calix[4] arene-Based n-Dialkylamino Extractants for Selective Platinum Group Metal Separation from Automotive Catalysts

To clarify efficiency recovery for platinum group metals (PGMs) from leach liquors of automotive catalysts, synthesis of three p-dialkylaminomethylcalix[4] arenes (propyl=1; butyl=2; and amyl=3), as extractants and their PGM extractabilities toward Pt, Pd, and Rh, from single-component PGM solutions, simulated mixed PGM solutions, and leach liquors of automotive catalysts were investigated. Various experimental conditions, such as the effect of shaking time, HCl concentration, concentration of extractants, and concentrations of Pd(II) and Pt(IV), were studied. The distribution ratio and stoichiometry ratio of Pd(II) and Pt(IV) extracted species were calculated. Extractants 2 and 3 showed a higher extractability compared to 1 toward Pd(II) and Pt(IV) ions from the leach liquors of automotive catalysts: E%=91.5% and 87.5% for 2, and 88.3% and 88.1% for 3, respectively. In contrast, the extractability of all the other metal ions (Al, Ba, Ce, La, Rh, Y, and Zr) by 2 and 3 was E%=<6%. Stripping of Pd(II) and Pt(IV) from organic solutions was achieved using a thiourea/HCl solution. Reusability of extractants 2 and 3 is also discussed.