Zinc Oxide Mineral Alkali Extraction Of New Technology Research,

Zinc oxide ore is a kind of refractory minerals, and it's difficult to be treated by mineral processing and smelting. Especially, the silica would inevitable form in acid aqueous process. For these reasons, a new process has been invented, which is used to treat zinc oxide ore in alkali aqueous process. This process mainly contains four procedures: Alkaline leaching Zinc oxide ore- Precipitating zinc with Na₂S and causticization of solution-Desilication using CaO-Leaching zinc oxide ore using desilicated mother liquor. The main content of this paper are as follows:(1) Alkaline leaching Zinc oxide oresThe lgc-pH diagram of Zn-Si-H₂O system is drawn and the thermodynamic conditions of alkaline leaching zinc oxide ore are analyzed. Zinc and silicon enter into solution in the form of Zn(OH)₄^2- and H₂SiO₄^2- respectively during leaching process.The kinetic of alkaline leaching zinc oxide ore is studied. The results of kinetic studies indicate that the calculated activation energy is 72.1 kJ/mol and the reaction order is 4.6, which illuminates that alkaline leaching zinc oxide ores is controlled by the chemical process of the reaction in the whole leaching process.The affecting factors, such as leaching temperature, holding time, alkaline concentration and ratio of liquid to solid (L/S), are used to study the leach of zinc oxide ores in NaOH solution. The results show that when the zinc oxide ores are leached for 2 h at 85℃in the presence of 5 mol/L sodium hydroxide with the L/S of 10:1, the leaching rate of Zn and Si are about 77% and 76%, respectively.(2) Precipitating zinc with Na₂S and causticization of solutionThe solubility of ZnO in NaOH solution is studied and the literature data is modified. The study shows that the effect of temperature on solubility is less than that reported by the literature.The lgc-pH diagram of Zn-Si-S-H₂O system is drawn and the thermodynamic condition of Precipitating zinc with Na₂S is analyzed. The process of precipitating zinc and causticizating the solution using Na₂S in alkaline solution is proposed.The experimental conditions, such as Na₂S dosage(S/Zn), precipitation temperature and reaction time are studied. Results show that when the molar ratio of S to Zn is 0.9:1, the reaction time is 10 minutes, the reaction temperature is 80℃, the precipitation rate of zinc is over 90%, while the concentration of zinc in the solution decrease to 3g/L from 25.75g/L.(3) Desilication of precipitated zinc mother liquorThe effects of CaO dosage, reaction temperature and reaction time were investigated in the process. The optimum experimental conditions are that the molar ratio of CaO to SiO₂ is 4:1, the reaction time is 1 hour, the reaction temperature is 85℃. Under the optimum conditions, the desilication rate is 90%, while the concentration of silicon in the solution decline to 0.5g/L from 5g/L.There are small amount of zinc in the desiliconization residues respect to total zinc in the leaching solution. The loss rate of zinc is just 4%.(4) Leaching zinc oxide ore using desilicated mother liquor.The study shows that the result of extraction using desilicated mother liquor is equivalent using flash NaOH stock solution. The NaOH solution can be recycled.As above, the recovery of zinc can satisfy requriment by the new process.