Comparative Study on Palladium(II) Extraction Using Thioamide-Modified Acyclic and Cyclic Extractants

For extraction from a single Pd(II) solution, 1,1′-bis[(dimethylthiocarbamoyl)oxy]-2,2′-thiobis[4- t -butylbenzene] ( 1 ) in a CHCl 3 diluent was found to exhibit a higher extractability for Pd(II) ions ( E % = 99.9%) in Cl – media (0.1 M) over 30 min as well as a higher extraction efficiency compared to 2,2′-thiobis[4- t -butylphenol] ( 2 ) as a starting material of 1 and macrocyclic compounds such as tetrakis[(dimethylthiocarbamoyl)oxy]thiacalix[4]arene ( 3 ) and p - tert -butylthiacalix[4]arene ( 4 ). Also, various parameters, such as the shaking time, diluents used, concentrations of Pd(II) and 1, effects of HCl, and effects of H + and Cl – ions, were studied. Extractant 1 could also be used for the selective extraction of Pd(II) ions ( E % > 99%) from the leach liquors of automotive catalysts that also contained the ions of Rh, Pd, Pt, Zr, Ce, Ba, Al, La, and Y in Cl – media and was found to be a more efficient extractant than 2 for Pd(II) recovery. In addition, the Pd(II) ions could be stripped from 1 using 0.1 M thiourea in 1.0 M HCl, thus enabling the reuse of 1 . Extractant 1 was actually found to exhibit a high E % for Pd (>96%) after five extraction cycles, indicating good stability in acidic media and potential usefulness for the rapid and selective recovery of Pd(II) from catalyst solutions in platinum group metal refineries.