Alkaline leaching Zn and its concomitant metals from refractory hemimorphite zinc oxide ore

Affecting factors, such as ore size, leaching temperature, holding time, alkaline concentration and liquid: solid ratio (volume/weight) (L/S), were studied to leach refractory hemimorphite [Zn4(Si2O7)(OH)·H2O] zinc oxide ores with NaOH solution in this paper. The impact of leaching recovery of Zn and its concomitant metals was checked through experiments. Results showed that when the ores of 65–76 µm size were leached for 2 h at 358 K in the presence of 5 mol/L sodium hydroxide and liquid:solid ratio of 10:1, the leaching rate of Zn, Al, Pb and Cd were about 73%, 45%, 11% and 5%, respectively, but that of Fe was less than 1‰. Moreover, the leaching experiments were repetitive and reliable. And the kinetic study indicates that the calculated activation energy is 45.7 kJ/mol, which illuminates that alkaline leaching the refractory hemimorphite [Zn4(Si2O7)(OH)⁎H2O] zinc oxide ores is controlled by the chemical process of the reaction of leach liquor and ores in the whole leach process.