| In our country large reserves of low grade zinc oxide ores bearing high basic gangues can not be treated by traditional zinc metallurgical process. In this dissertation, a new process named as MACA method was proposed to produce cathode zinc from these zinc oxide ores in the system of Me-NH4Cl-NH3-H2O.Theoretical and technical studies on the extraction zinc in Me-NH4Cl-NH3-H2O (MACA) system were carried out in detail and some meaningful conclusions were obtained.Thermodynamics of Zn(Ⅱ) complex equilibria in Zn(Ⅱ)-NH3-Cl--CO32--H2O system was studied based on the conservation of mass and charge neutrality. When the concentration of ammonia and ammonium chloride is variable in range of 0-5mol/L, the equilibrium concentrations of all species were calculated, respectively, and thermodynamic diagrams were plotted. It indicated that the total equilibrium concentration of zinc is enhanced with the increasing of ammonia concentration in presence of CO32- ion. The theoretical calculation results were testified by solubility experiments. The results show that the average relative error is less than 8%, which indicates that the thermodynamic models and critical data are feasible and reliable.The behavior and equilibrium law of major impurities, such as Cu, Cd, Co, Ni, Pb and Mg, during the leaching of zinc oxide ores in Zn(Ⅱ)-NH4Cl-NH3-H2O system were detailedly analyzed. Cu, Cd, Co, Ni and Mg in raw material can be leached out with certain rate due to the formation of metallic complex like Me(NH3)in+,Me(OH)jn-j,or MeClkn-k. The impurities in leaching solution have adverse effect on zincelectrowinning, and must be removed.The difficulties or ease of removal major impurities from Zn(Ⅱ)-NH4Cl-NH3-H2O system were systematically revealed by potential-concentration diagrams. The potential differences between EMe2+/Me(Me represent Cu2+,Ni2+,Pb2+,Co2+) and EZn2+/Zn are higher than0.4V when the concentration of ammonia and ammonium chloride is variable in range of 0-5mol/L, respectively. So they can be cemented thoroughly by zinc powder. When the concentration of ammonia and ammonium chloride is higher,the potential differences between EMe2+/Me (Me represent Cu+,Cd2+) and EZn2+/Zn are low, and the minimum value is 0.16V.ECd2+/Cd,ECo2+/Co is close to EH+/H2,cadmium and cobaltcemented will not resolve in Zn(Ⅱ)-NH4Cl-NH3-H2O system at ambient temperature.Leaching kinetics of zinc oxide ore in the system of NH4Cl-NH3-H2O was studied. It is indicated that diffusion through the inert ash film is the controlling step. The leaching kinetics follows shrinking-core model, and the apparent activation energy is about 7.057 kJ/mol. Dynamical equation can be expressed as follow:A new process of "cycle leaching-purification-electrowinning" in the system of Zn(Ⅱ)-NH4Cl-NH3-H2O was proposed for extracting zinc from the zinc oxide ores bearing high basic gangue. Zinc concentrations in the obtained pregnant solution may be met the case of zinc electrowinning. Spent electrolyte was recycled to leaching operation. The whole process was carried out at ambient temperature and the direct-current consumption was low. So it is a cleaning and energy-saving process for zinc hydrometallurgy. Middle and low grade zinc oxide ores from Lan-ping in Yunnan province were used as raw materials in present dissertation and wonderful results were obtained.Middle-grade zinc oxide ores from Lan-ping were leached under the following optimum conditions: total ammonium concentration of 7.5 mol/L,nNH4Cl/nNH3=2:1,the ratio of liquid to solid being 4, mechanically stirring speed of 300 rpm, leaching time for 60min at ambient temperature. The average leaching rate was 88.57%, and the average concentration of zinc in pregnant solution was 43.20g/L. During heaping leaching, the composition of lixiviant was the same as bottle leaching, and the leaching rate of zinc was 92.19% after 30 days at ambient temperature when the ratio of liquid to solid is 2.5.The concentration of As and Sb in pregnant solution can be decreased to 0.3 mg/L by colloid coprecipitation method. After two-stage of counter-current cementation by zinc powder, the concentration of impurities, such as Cu, Cd, Co, Ni and Pb, may be less than 1 mg/L, respectively. The obtained purificatory solution meets the requirements of zinc electrowinning.The additives have significant influence on the surface morphology of cathode zinc. Sponge zinc was produced during zinc electrowinning without additives. Compact zinc plate can not be obtained when electrowinning adding any one or two of additives as bone glue, T-B and T-C. Compact zinc plate was obtained when the amount of bone glue, T-B and T-C is 100mg/L,100mg/L and 2ml/L, respectively.According to the results of single-factor experiments, the optimum conditions of zinc electrowinning was determined as follow: electrode space of 3 cm, current density of 400A/m2,zinc concentration in spent electrolyte >15g/L, bone glue of 100mg/L, T-B of 100mg/L, T-C of 2ml/L,and at 40℃.Cathode zinc obtained under optimum conditions meets the requirements of first-grade zinc in GB 470-1997 1# standard. Current efficiency was higher than 90%. The power and ammonia consumption was about 2882 kWh/t zinc and 0.2 t/t-zinc, respectively. Spent electrolyte was recycled to leaching operation after its composition adjusted. The results show that spent electrolyte circulation hasn't adverse influences on the technical and economic indexes of the process.During leaching low-grade zinc oxide ores, the concentration of zinc in leaching solution was enriched continuously by the method of circulation leaching. After five-cycle of lixiviant, the concentration of zinc in leachate was higher than 37g/L under the conditions that total ammonium concentration is 6 mol/L,nNH4Cl/nNH3=1:1,the ratio of liquid to solid is 4, mechanically stirring speed is 300rpm, and leaching time for 3h at ambient temperature. The average leaching rate of zinc was 98.47%. The purification and electrowinning of obtained leachate was carried out under the above-mentioned optimum conditions. The concentration of impurities, such as As, Sb, Cu, Cd, Co, Ni and Pb in purificatory solution may be less than 1mg/L. Cathode zinc obtained meets the requirements of first-grade zinc in GB 470-1997 1# standard. Current efficiency was higher than 90%. The power and ammonia consumption was about 2991 kWh/t·zinc and 0.2 t/t-zinc, respectively.
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