Basic Theory Research On Alkaline Process Of Extracting Zn From Zinc Oxide Ores

With the increase of China's demand of zinc source and the increasingly shortage of zinc sulfide, zinc oxide ore resources are gradually getting developed and utilized. This article carried out some basic theory research to the new of technology of zinc oxide alkaline leaching. The specific research content are as follows.1) The article investigated the dissolving balance time of ZnO in different Na2O concentration, plotted Na2O-ZnO-H2O system equilibrium diagram at 25℃,50℃,75℃and 100℃, and found Na2O-ZnO-H2O system equilibrium diagram is component of rising curve segment (the left half curve) maximum solubility point and the decline curve segment(the right half curve). The solid-phase on the left half curve of Na2O-ZnO-H2O system equilibrium diagram is ZnO while the one of the right half curve is NaZn(OH)3. There is little difference in ZnO solubility of Na2O-ZnO-H2O system among 25℃,50℃,75℃and 100℃in low alkali concentration (Na2O%< 29%) and it is possible to realize the separation of ZnO by diluting. But ZnO solubility differs quite a lot with temperature in high alkali concentration and it's also possible to separate NaZn(OH)3 from the equilibrium system by cooling down.2) Results showed it is able to get needle-like NaZn(OH)3 crystals when Na2O-ZnO-H2O system in high alkali concentration cools down. Cooling crystallization changes with the initial alkali concentration. With the cooling rate increasing, the crystallization rate of the same system also increases and gets to equilibrium state earlier; however, when it gets to the same temperature, the crystallization ratio becomes lower, but the gap gets narrower as temperature cools down and disappears finaly at the end temperature for enough long time. Research investigated isothermal crystallization through four cooling rate experiments, characterized it with dynamics crystallization model and got 3 series dynamic parameters. Results shows Avrami and R-t methods are able to describe isothermal crystallization. Although Ozawa equation can also get good linear relation for this reaseach, it is not applicable to describe the isothermal crystallization of Na2O-ZnO-H2O system. 3) Research declared Na2O-ZnO-H2O system crystallizes virgate ZnO crystal by diluting with water. The larger the dilution factor is, the thinner ZnO crystal is and the crystallization ratio will also increase though the increasing scope decreases. As the diluting temperature goes up, ZnO crystal becomes thicker and the crystallization rate goes up too.4) Research discussed the effection of SiO2 and CaO on Na2O-ZnO-H2O system, found that the ZnO maximum solubility point of Na2O-ZnO-SiO2-H2O system moves toward higher Na2O and ZnO concentration point and the decline rate of the corresponding right half curve reduces as the n(Na2O)/n(SiO2) value grows up. After Ca(OH)2 is added to Na2O-ZnO-H2O system, ZnO solubility in alkali solution of which the Na2O concentration is under 15% reduces and the decline becomes narrow along with the temperature. Results show CaO does greater influence to ZnO solubility in Saturated zinc sodium solution than Ca(OH)2 does.5) Research showed the efficiency of CaO removing SiO2 from Na2O-ZnO-SiO2-H2O system rises with amount of CaO, but the zinc loss ratio goes up too.1.5 times of theoretical additive amount of CaO is most suitable. Desilication efficiency of CaO is remarkablely influenced by temperature:the higher, the better. Meanwhile zinc loss ratio declines. Desilication efficiency of CaO increases with time and it achieves a good result in 90 minutes or so.