Extraction and recovery of zinc and indium from residue rich in zinc ferrite

• Liquid-solid ratio, temperature and acid concentration are vital for In extraction. • Alkaline leaching was found to be selective for zinc extraction. • Oxalic acid addition significantly increased indium extraction. • Multiple step leaching enhanced the indium concentration in aqueous solution. • Addition of small amount of NaOH with Na 2 CO 3 resulted in 8% indium in precipitate. Indium is regarded as critical metal due to its scarce availability and increasing demand. The extraction of indium from primary sources is important as an effort to alleviate indium availability given its potential role in sustainable technological advancement. This study introduces a process based on zinc ferrite reduction for the extraction of indium in addition to zinc from zinc residues. Zinc ferrite in zinc residue was partially reduced at 600 °C with a reducing gas containing 10% H 2 and the roasting product was subjected to leaching at various conditions to study extraction of target elements. Decomposition of zinc ferrite led to a significant increment on the leaching kinetics of zinc residue. Multiple-step leaching was also explored to enrich the indium concentration in aqueous liquor followed by precipitation of indium. A maximum of 0.121 g/L indium concentration was obtained in multiple step leaching. The effect of temperature, acid concentration, liquid–solid ratio (L/S) and oxalic acid addition on leaching has also been discussed. The proposed process yields an aggregate of about 89% and 88.3% Zn and In extraction respectively along with significant indium concentration in the aqueous leach solution. The precipitation of synthetic solution showed that indium can be precipitated to obtain a concentrate containing about 8% In.