Palladium extraction with N,N,N′,N′-tetra-n-octyl-thiodiglycolamide

The extractability of Pd(II) using N,N,N′,N′-tetra-n-octyl-thiodiglycolamide (TOTDGA) diluted with a mixed solution of n-dodecane and 2-ethylhexanol and the durability of TOTDGA against a strong acid solution (0.75 M HNO3–2.25 M HCl) were investigated by solvent extraction and FT-IR measurements, then compared to those using the conventional extractant, di-n-hexyl sulfide (DHS). The dependence of the extraction percentages of some platinum group and base metal ions (Pd(II), Pt(IV), Rh(III), Fe(III), Cu(II), Ni(II) and Zn(II)) on the HCl and TOTDGA concentrations shows that a good selectivity for Pd(II) extraction is obtained at [TOTDGA] ⩽ 0.2 M–[HCl] ⩽ 3 M. The Pd(II) extraction from 1 M HCl with 0.1 M TOTDGA is much faster than that with 0.1 M DHS. The loading capacity of Pd(II) is about 7 g/L using 0.1 M TOTDGA, which is comparable to that using DHS. The Pd(II) extracted in the TOTDGA is effectively back-extracted by an ammonia solution, although its efficiency depends on the condition of the forward extraction and metal concentration in the organic phase. In the durability test, the extraction percentage of Pd(II) and the FT-IR spectra were measured using TOTDGA and DHS after stirring with 0.75 M HNO3–2.25 M HCl solutions. The extraction percentage of Pd(II) with TOTDGA hardly changes after a one-week stirring (∼100%), while that with DHS drops from ∼100% to ∼65%. The FT-IR spectra show sulfoxide formation by the oxidation of the sulfide in DHS after the stirring, but not in TOTDGA, indicating that TOTDGA is more durable than DHS.