Leaching of zinc from calcined smithsonite using sodium hydroxide

The processes of calcination and alkaline leaching were applied to treat a zinc oxide ore, smithsonite (ZnCO3). The phase evolution in the calcination was studied, as well as the effect factors on the leaching rate of Zn, such as calcination temperature, alkaline concentration, phase ratio of liquid to solid (L/S), leaching temperature and leaching time. It was found that the ZnCO3 had completely decomposed into ZnO when calcined for 2 h at 400 °C and the Zn leaching rate of ores calcined at 400 °C could be over 92% with 20% (6.25 mol/L) sodium hydroxide and a phase ratio of 80:1 for 4 h at 100 °C.