Solvent extraction and separation of zinc-iron from spent pickling solution with tri-n-octylamine

Studies on the effective extraction and separation of zinc-iron from spent pickling solution using tri-n-octylamine (TOA) with solvent extraction were investigated. Single extraction efficiency of 83.75% is obtained under the optimal conditions (organic phase consisting of 30% (v/v) extractant TOA, 20% (v/v) modifier iso-octanol, and 50% (v/v) diluent sulfonated kerosene, organic phase volume: aqueous phase volume of 2:1, and extraction time 10 min), while only 1.8% iron is co-extracted. McCabe-Thiele diagram is employed to analyze the number of theoretical stages needed for the effective extraction of zinc, and it is found that under five-stage counter-current extraction, almost all the zinc ions are extracted. A stripping efficiency of more than 90% from the loaded organic phase is achieved by 2.0 mol/L NH₃·H₂O and organic phase volume: aqueous phase volume of 1:2. Furthermore, the extraction mechanism of zinc with TOA accompanied by anion exchange is demonstrated by FT-IR spectra analysis and ESI-MS analysis, and the structure of the extracted complex is confirmed as [R₃NHZnCl₃].