Solvent extraction of zinc by 2-hexylpyridine in benzene from aqueous mineral acid - thiocyanate media

Solvent extraction of Zn(II) by 2-hexylpyridine (HPy) in benzene from aqueous mineral acid - thiocyanate media has been studied. The extraction was followed by 65Zn tracer. The extraction, though dependent on the acidity of the aqueous phase, is poor from mineral acids (HCl, HNO3 or H2SO4). Addition of 0.02M KSCN to the aqueous phase enhances the distribution ratio by a factor of almost one thousand. The stoichiometry of the extracted complex established by the usual slope analysis method indicates that an ionic type complex, e.g. Zn(SCN)4x(HPyH)2, is responsible for the extraction. Complexing anions like acetate, oxalate or citrate at 1M concentration mask the extraction of Zn(II) almost completely. Separation factors determined at optimal conditions (0.1M HPy in benzene - 0.05M H2SO4+0.2M SCN-) indicate that Zn(II), along with Hg(II), can be separated in a single extraction from a number of metals, e.g. Cs(I), Sr(II), Ln(III), Y(III), Cr(III) and Cr(VI). Other metals of interest like Cu(II), Co(II), Fe(III), Mo(VI), U(VI) and Tc(VII) are coextracted but the separation factors are large enough to allow separation in a multistage extraction process. (author)