Materials balance of pilot-scale circulation leaching of low-grade zinc oxide ore to produce cathode zinc

The pilot-scale production of cathode zinc from low-grade zinc oxide ore through periodic extraction in NH3–NH4Cl–H2O system was studied. Leachant balance in circulation process was controlled by parameters of recycling rate (γ) and relative concentration error (De) between CMeLn and CMeL∞ according to the equation . The concentration of zinc in leach liquor was enriched in 39·085 g/L after five recirculation leaching cycles, which was consistent with the predicted value theoretically when recycling rate was supposed to 0·467.Cathode product containing more than 99·9% of Zn and current efficiency of 97·02% were obtained after purification of two-stage treatment. The liquid loss was confirmed to exist in electrowinning operation and the problem of solution balance was solved through partial diverging cycle and addition of washing water in residue washing unit. Mineralogical analysis results showed that about 90% of ammonia-soluble Zn (ZnCO3 + ZnSO4) dissolved out from zinc ore.