Extraction of palladium(II) from nitric acid solutions with diglycolthioamide

• Novel diglycolthioamide (DGTA) extractants were synthesized for the recovery of palladium in nitric acid for the first time.
• The extraction behaviors of DGTA for Pd(II) in nitric acid solution were investigated in detail.
• DGTAs exhibit great extraction power and high selectivity for Pd(II).

Two novel diglycolthioamides, 2-(2-(dioctylamino)-2-thioxoethoxy)-N,N-dioctylacetamide (mono-TODGTA) and 2,2′-oxybis(N,N-dioctylethanethioamide) (di-TODGTA), were synthesized and characterized by MS and 1H NMR. Their solvent extraction behaviors for Pd(II) in nitric acid solutions were investigated by using kerosene as diluent. Effects of concentration of nitric acid and extractants on the extraction percentage of Pd(II) were examined. Both of the two extractants show high extraction efficiency and selectivity for Pd(II). By comparison, di-TODGTA exhibits higher selectivity than mono-TODGTA. By means of mole ratio method and Job's method, Pd(II) was found to be extracted as mono-solvated and semi-solvated species for mono-TODGTA and di-TODGTA, respectively. The extraction equilibrium constants for mono-TODGA and di-TODGTA are Kex,mono = 1.39 × 108 and Kex,di = 3.95 × 1014, separately. Complete back extraction of palladium can be achieved by thiourea.