Solvent extraction and separation of zinc and iron from spent pickle liquor

Abstract

The present study reports liquid-liquid extraction and separation of zinc and iron values from a spent pickle solution. Tertiary amine viz. tri-iso-octyl amine (TiOA) or tris(2-ethylhexyl) amine (TEHA), in the absence and presence of di-(2-ethylhexyl)phosphoric acid (HDEHP), has been used for the separation of zinc and iron. Three aqueous solutions were investigated: i) HCl–Fe(II)–Fe(III), ii) Zn(II)–HCl, and iii) HCl–Fe(II)–Fe(III)–Zn(II) with the composition similar to that of pickle liquor (g/L) [117 Zn(II), 90 HCl, 30 Fe(II) and 1 Fe(III)]. Co-extraction of Zn(II), HCl and Fe(III) was noticed with the extractants (amine/amine + HDEHP) without any appreciable selectivity except for Fe(II) which was not extracted by the solvent. Zn(II) was extracted selectively leaving Fe(II) in the raffinate provided that Fe(III) was removed from the solution at a low O/A phase ratio or reduced to Fe(II) state. Stripping of HCl, Zn(II) and Fe(III) was also not selective with distilled water. The Zn(II) free raffinate containing Fe(II) was microbially oxidized to Fe(III) and was then quantitatively extracted in 3-stages with 30% Versatic 10 acid at the O/A phase ratio of 3.5:1. Loaded Fe(III) was easily stripped from the organic phase with dilute sulfuric acid. A flowsheet is proposed to produce high purity Zn(II) and Fe(III) solutions by solvent extraction.