| Zinc hydrometallurgy plant produce large amounts of germanium-containing zinc oxide fume during a production process in Yunnan Province.The present art of dust treatment is sulfuric acid leaching and tannic germanium precipitation for recovering Ge. For insoluble of Fe4Ge3O12, the leaching rate of germanium is generally lower than60%. Thus, separation and destruction of Fe4Ge3O12becomes a key technical subject for improving germanium extraction and the efficient utilization of germanium resource. Microwave treatment has the capability of reducing the particle size of minerals, increasing their specific surface area, and even transforming their crystal structures. Two novel processes of microwave roasting are proposed for improving Ge extraction in this dissertation, and their key technology and related theories are studied. Results reveal that Ge leaching rates are markedly increasedAt first, microwave calcination-sulfuric acid leaching was used to recover Ge. The size of material reduces the specific surface area and the Ge extraction increase with increasing temperature, when the microwave sintering temperature is in the range of210℃～290℃. It is unfit for leaching of germanium when the temperature is higher than290℃. The average particle sizes of zinc oxide dust bearing germanium reduce from5.39μm to1.70μm after microwave calcination at290℃for10min. The Ge extraction increased after microwave calcination because the particle size became small. The SEM and XRD of material show microwave calcination can change the morphology and particle size of zinc oxide dust bearing germanium. Large particle was fragmentated, the size of zinc oxide dust bearing germanium was reduced, the uniformity of size was improved, and the characteristic peak of Fe4Ge3O12was disappeared after microwave calcinations. The relational mode of the germanium extraction and the influencing factors was obtained by Design-Expert software. Microwave calcination temperature, liquid-solid ratio and initial concentration of sulfuric acid are the significant factors for the process. Microwave calcination-sulfuric acid leaching experiments was designed using response surface methodology. By analyzing each factors significance and the correlation, the optimized conditions were obtained as follows:microwave calcination at287℃, liquid-solid ratio of6.5mL·g-1, leaching time of4h, sulfuric acid initial concentration of9.0mol/L, leaching temperature at60℃with germanium extraction about84.37%. The predictive value was85.25%. The relative error is1.04%between the forecast value and the actual value. The germanium extraction was increased22%compared with existing process. The kinetics of Ge leaching by microwave calcination-sulfuric acid was studied. The effects of leaching temperature and initial concentration of sulfuric acid on the leaching rate of germanium were examined. The experiment results indicate that germanium leaching rate increases with increasing temperature and initial concentration of sulfuric acid. It was found that the reaction kinetic model follows the shrinking core model of the diffusion process of the solid film.Microwave alkaline roasting-water dissolving process was proposed to further improve the germanium extraction. The germanium extraction is consistent with the linear polynomial model type. Alkali-material ratio, microwave heating temperature and leaching temperature are the significant factors for the process. By analyzing each factors significance and the correlation, the optimized conditions were obtained as follows, alkali-material ratio of1g·g-1, aging time of1day, microwave heating at408℃, microwave alkaline roasting holding time of10min, liquid-solid ratio of6.4mL·g-1, leaching temperature at66℃, leaching time of67min with the germanium extraction about97.38%. The predictive value was97.16%. The relative error is0.23%between the forecast value and the actual value. Compared with the existing methods, the alkaline roasting temperature was reduced from1080℃to408℃and the alkaline roasting holding time was greatly reduced from60min to10min.The kinetics of germanium leaching by microwave alkaline roasting-water dissolving was studied. It was found that the dissolution reaction kinetic model follows diffusion control. The apparent activation energy is15.46kJ/mol. Basing on the study of Artificial Neural Network, the neural models were established for the prediction of microwave calcination-sulfuric acid leaching and microwave alkaline roasting-water dissolving. The results indicated that the neural network prediction model of microwave calcination-sulfuric acid leaching and microwave alkaline roasting-water dissolving were reliable, the forecast and actual values fitted well. The model could be used to predict the regeneration experiments with high credibility and practical significance. The accuracy of convergence of two models has reached10-5. |
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