Liquid-liquid extraction of palladium(II) from chloride media by N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide

Previous research showed that N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide (DMDCHTDGA) in 1,2-dichloroethane is able to co-extract platinum(IV) and palladium(II) from concentrated hydrochloric acid solutions. Following a detailed study about Pt(IV), the present work focuses on the thorough investigation of Pd(II) extraction by DMDCHTDGA in toluene. The removal of Pd(II) is rather efficient from 0.5 M to 5.5 M HCl, and progressively decreases until 7.5 M HCl. Pd(II) stripping is better achieved by an acidic thiourea solution, but ammonia aqueous phases can alternatively be used for some cases. Pd(II) extraction kinetics is relatively favored (5-15 min). The robustness of DMDCHTDGA to extract Pd(II) has been confirmed through five successive reutilization experiments. The maximum loading capacity for Pd(II) reaches a 2.5 DMDCHTDGA:Pd(II) molar ratio. Pd(II) can selectively be recovered by DMDCHTDGA from 4.0 M or 6.0 M HCl complex mixtures containing equivalent concentrations of Pt(IV) and Rh(III), and fivefold Fe(III) and Al(III) concentrations, although with a slight Pt(IV) contamination.