Novel dithioamide extractant for highly selective separation of Pd from acidic leach liquors of waste auto-catalysts

The development of novel efficient extractants for Pd recovery from high acidic chloride media leaching solutions has always been an important task. In this study, a novel pincer extractant N,N'-dibutyl-m-phenyldithioamide (DBTB-4) was successfully synthesized, and its structure was confirmed by FT-IR, 1H NMR, 13C NMR (DEPT 135), ESI-HRMS and EA. The possibility of Pd recovery from leaching liquors of waste auto-catalysts by DBTB-4 was evaluated. The Pd extraction mechanism by DBTB-4 from chloride media was studied. DBTB-4 has rapid extraction kinetics for Pd (<30 min), strong extractability and specific selectivity for Pd at acidity of ≤4 mol per L HCl. There are no precipitants or a third phase generation during Pd extraction using a mixture of kerosene and isooctanol with V kerosene/V isooctanol of 1 : 3 as diluent. DBTB-4 quantitatively extracts Pd with DBTB-4/Pd molar ratio of 1 : 1 through coordination with Pd via the two S atoms and the carbon in the phenyl between the two thioamide groups forming two five-membered chelate rings. The extracted complex can be written as (L-H)PdCl, where L stands for one molecular of DBTB-4. DBTB-4 can quantitatively and selectively extract Pd from leaching liquors of waste auto-catalysts leaving nearly all Pt, Rh and base metals in the raffinate.