Microwave-Aided Leaching Of High Silica Zinc Oxide Ores

Zinc sulfide and zinc oxide are two main mineral forms existing in zinc ores. The processing of zinc oxide ores is becoming more attractive due to the depletion of zinc sulfide ores. Usually, zinc oxide ores contain much SiO2 and in the process of direct sulfuric leaching, SiO2 may dissolve in leaching solution and cause ore pulp difficult for solid liquid separation. Therefore, research on sulfuric acid leaching of high silica zinc oxide ore focuses on how to improve filtration performance of ore pulp.In this thesis, behavior of SiO2 dissolving from ore as well as the effect of colloidal SiO2 on separation performance of ore pulp was investigated. Through experiments, the mechanism of sulfuric acid leaching of high silica zinc oxide ores was confirmed to a certain extend. The effect of microwave heating on separation performance of ore pulp and the leach process was also investigated, by and large, the role of microwave heating in leaching was determined. Then based on above results, microwave heating was introduced into leach process of zinc oxide ores safely to present a new technology.Colloidal SiO2 concentration, pH, temperature, electrolyte, precipitant and agitation condition are the main factors affecting separation performance. Through experiments, the parameters affecting separation performance were found out basically. It was learned that when pH equals 5 and the ore pulp is heated for approximately 15 minutes, the boiling ore pulp containing 3-6 g/1 SiO2 will be easy to filter and Zn2+ of lower than 100 g/1 has no influence on filtration and colloidal precipitation. It indicates that colloidal Si02 can be reduced to a level of lower than 0.5 g/1 without any precipitant and only through intensive stirring can ore pulp of excellent separation characteristics be achieved.Examining the results of experiments heated by conventional electric stove and microwave furnace contrastively, it can be concluded that microwave has no obvious influence on separation performance and the leach process. At the same time, as a clean and efficient heating technique, microwave heating can considerably reduce the energy consumption of metallurgical process. Therefore, it is efficient to introduce microwave heating into zinc hydrometallurgy without any side effect.Referring to the current technology of neutralization and coagulation, operating flow and controlling parameters of the new technology were demonstrated in this thesis. Extraction percentage of Zn is greater than 96% while those of SiOi and Fe less than 1.3% and 0.05% respectively. Obviously, the main metal element is separated from impurities efficiently while an ore pulp easy to filter is obtained.The new technology of microwave-aided leaching lasts short time, consumes low energy and is convenient to controlling. The process of desiliconization will not bring any impurities because ground ore is added as neutralize agent and no precipitant is used. After conventional concentrating and purifying, the filtrate can be electrolyzed directly. Low efficiency and high pollution are common problems existing in middle or small scale zinc hydrometallurgical plants, the technology of microwave-aided leaching provides a feasible solution to these problems. The study of microwave-aided leaching deepens our understanding of desiliconization mechanism in leaching and presents a valuable reference for research of microwave hydrometallurgy and sulfuric acid leaching of high silica zinc oxide ores.