IRON REJECTION THROUGH JAROSITE PRECIPITATION DURING ACID PRESSURE LEACHING OF ZINC LEACH RESIDUE

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+, NH4+ 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+ > NH4+ > K+.