Iron rejection through jarosite precipitation during acid pressure leaching of zinc leach residue

Abstract

Electrolytic zinc processes produce leach residues containing 15–18% zinc and 27–37% iron. In India large quantities of such residues are stock-piled at zinc plants. During leaching of a typical sample of stock-piled residue it was observed that at 463 K the sulphuric acid leaching gave 30–50% iron dissolution with 80–85% zinc extraction. To minimize iron dissolution, high temperature sulphuric acid leaching with simultaneous rejection of iron through jarosite precipitation was carried out in the presence of the monovalent cations Na +, NH 4 + and K +. It was possible to reject 80% of the dissolved iron as jarosite without affecting zinc extraction. The efficiency of the cations for iron rejection was in the order Na + > NH 4 + > K +.