| Abstract Scope |
Solvent extraction is widely used for the separation and purification of platinum group metals (PGMs). We have studied the extraction of PGM ions from HCl solutions and found promising extractants for Pd(II) and Rh(III), respectively. Sulfide-diamide-type thiodiglycolamides (TDGAs) extract Pd(II) chloridometalates much faster than the conventionally used di-n-hexyl-sulfide (DHS). In addition, TDGAs show high stability against strongly acidic solutions, unlike DHS. The Pd(II) extracted with TDGAs can be stripped with aqueous ammonia. As for Rh(III), amide-containing tertiary amines (ACTAs), especially diamide-type and triamide-type ACTAs, efficiently extract Rh(III) in 1-5 mol/L HCl solutions, although a pentachlororhodate, [RhCl5(H2O)]2-, which is a typical unextractable complex, is dominantly present in these solutions. The high extraction efficiency would stem from the outer-sphere coordination assemblies that comprised the [RhCl5(H2O)]2- and protonated ACTAs. The loaded Rh(III) in the ACTAs can be stripped with a highly-concentrated HCl solution or NaOH aqueous solution. |