| Zinc oxide ore are stepwise developed and utilized along with the rapidly consumption of zinc sulfide ore resources.It is comparatively suitable to leaching high-alkaline gangue zinc oxide ore with ammonia-ammonium -water system,which has been carried out a lot of research.In the zinc oxide ores,zinc exists in the form of zincite,smithsonite, hydrozincite,willemite and hemimorphite,et al.It had been accepted that it's easy to leach zinc oxide and zinc carbonate with ammonia-ammonium -water system.But there was few researches on zinc silicate such as hemimorphite,also there were different opinions on its leaching behaviors.Many researchers held that it is hemimorphite can't be dissolved that made the low leaching ratio of zinc oxide ore.Thus,it is of great academic and application value to research on leaching thermodynamics and behaviors of hemimorphite with ammonia-ammonium -water system.Leaching of hemimorphite with NH3-(NH4)2SO4-H2O was studied using pure hemimorphite as the raw material in this paper.The thermodynamics of Zn4Si2O7(OH)2·H2O-NH3-(NH4)2SO4-H2O system was analysised and the dissolve equlibrium diagram of zinc in hemimorphite and silicon were drawn.Zn(NH3)42+ was stable when the concentration of total ammonia is 8.5 mol/L,pH value is at the range of 6.2～12.8,and the total Zn concentration reached its maximum when pH value is 9.2.Si respectively existed in the form of H4SiO4(aq),H3SiO4-, H2SiO42- when pH value is less than 9.6,at the range of 9.6～11.8,more than 11.8.The equilibrium concentration of Zn increased rapidly with increase of the total concentration of ammonia;The concentration of Si had no obvious change as it reached saturation and precipitated solid silicate,all kinds of silicate ion transformed to H2SiO42- step by step and the total concentration of Si increased when pH value increased further. The equilibrium concentration of Zn reached its maximum when [NH3]/[N]T was 0.5.The effect of total ammonia concentration,reaction time,ammonia/ ammonium molar ratio,temperature,stirring speed and other factors on leaching ratio were investigated and the results showed that when hemimorphite is leached with NH3-(NH4)2SO4-H2O system,total ammonia concentration was the main influence of zinc leaching ratio and the rate was low with pure ammonia or pure ammonium sulfate system, which matches thermodynamic results well.Leaching ratio of zinc could achieve 93.84%when total ammonia concentration is 8.5 mol/L,molar ratio of NH3 to(NH4)2SO4 is 2:1,liquid/solid ratio is 20,stirring rate is 250r/min and leached 1 h at 45℃.This study showed that leaching hemimorphite with NH3-(NH4)2SO4-H2O system was feasible in thermodynamics,also the leaching speed was quite fast.Silicon of hemimorphite entered into leaching residue in the form of SiO2·2H2O after leaching under the experiments condition.The leaching reaction is:Zn4Si2O7(OH)2·H2O(s)+ 8NH3(aq)+8NH4+→4Zn(NH3)42++SiO2·2H2O(s)+2H2O.
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