| This paper is a preliminary study for the leaching process and mechanism under the complex system of ammonia leaching of high grade zinc oxide. Relying on the National Natural Science Foundation of supervisor, in which, the refractory low-grade zinc oxide ore ammonia dissolution leaching-leached flotation tests and the relevant mechanism have been completed of early in the project and obtain the relevant results. However in the early course of the study, high-grade zinc oxide ore with a certain amount of zinc sulfide often occur. In order to explore the mechanism of ammonia leaching behavior of such mines, and also as a useful supplement to the preliminary study, a more comprehensive understanding of behavior and mechanism of each grade interval of oxidation zinc, ammonia leaching of high grade zinc oxide should be studied. In this paper, the object is the Lanping zinc oxide, in which the zinc content was 40.61% and the oxidation rate is 78.72%. Just from the grade, the class ore alternative processing methods are many, but to explore the mechanism, the paper has certain theoretical value, and can enrich the theory of ammonia corrosion of zinc oxide ore leaching in some sense.At first, the effect of low total ammonia concentration and high total ammonia concentration on the leaching process were studied. Three different ammonia solution leaching system were used, including single ammonia leaching system, ammonia-ammonium fluoride leaching system and ammonia-ammonium sulfate leaching system. The results show that the dissolution trends of three kinds of leaching system in ammonia leaching were generally consistent. But the leaching index is different; it is different with ammonia leaching rules on low grade zinc oxide ores. The best extraction effect is single ammonia leaching system with the zinc leaching rate of 39.42% and the leaching rate of zinc is 73.47%. Ammonia-ammonium fluoride leaching system is second. And the leaching rate is closed to the first one at a high concentration of total ammonia with the zinc leaching rate of 39.33% and the leaching rate of zinc is 73.29%. Ammonia-ammonium sulfate effect is the worst with the zinc leaching rate of 30.88% and the leaching rate of zinc is 57.55%. In addition, the effect of the liquid to solid ratio and leaching temperature on leaching rate is significant by testing on the leaching factors, including liquid solid ratio, ammonia ammonium ratio, stirring speed, leaching time, leaching temperature and grinding fineness.In this paper, the SEM-EDS, XRD and XPS techniques were carried on to study the difference leaching residue from ammonia leaching system, ammonium sulfate leaching system, ammonium fluoride leaching system, ammonia-ammonium fluoride leaching system and ammonia-ammonium sulfate leaching system in leaching theory research. By the test results of instrumental analysis, it was found several conclusions, such as:for single ammonia leaching system, on the surface of leaching residue, the signs of erosion are obvious, and cracks appeared on alignment in the same time. These cracks are also showing smooth crystal surface, indicating that leaching is carried out along certain planes. For ammonia-ammonium fluoride leaching system, leached surface is wrapped by spherical particles and micro-fine ore etc. Combined with the thermodynamic analysis of the leaching process, it is found that the main effect material of zinc mineral leaching is the amorphous silica, the mainly occurred in the system reaction is likely to be dominated by hydroxyl coordination reaction with a larger pH value, and the ammonia as the leading method with the lower pH value by though the preliminary analysis of test results of the instrument and mineral thermodynamic behavior in the leaching effect and leaching process. It explains the differences between high and low grade ore leaching results of zinc oxide and make a preliminary supplement on the integrity of zinc oxide ammonia leaching of ore dissolution by studying on the ammonia leaching mechanism on the high grade zinc oxideResearch to arrive at a conclusion that is amorphous silica is the main effect material of zinc mineral leaching is the amorphous silica. The concentration of total silicon in solution ([Si]x) will increase together with the total ammonia concentration, and the other form of ion concentration will also increase except the concentration of H4SiO4 unchanged. The advantages of the components present in the system may be Si3O5(OH)53-、H3SiO4-、Si2O3(OH)42-.Finally, the paper carried out coordinated research of dissolution in ammonia leaching process of willemite and calamine. After leaching process of calamine and willemite, the coordination compounds of Zn2+ mainly in the same pH range, and when only consider the leaching of zinc ions, the leaching behavior independent of the mineral anion. Under neutral or acidic conditions, willemite is mainly presence in the form of Zn2+ and Zn(NH3)32+. When the pH is raised to 9.246, Zn2+ is mainly presence in the form high ligand complexes of zinc ions. Since the experiment involved a high total ammonia concentration leaching system, the pH of single ammonia leaching system is high, according to thermodynamic calculations, Zn2+ coordination reaction may be led by hydroxyl and generate high-coordinating such as Zn(OH)64-; however ammonia-ammonium fluoride leaching system is buffer solution with a stable and low pH value. The Zn2+ coordination reaction may be led by the amino or amino and hydroxyl. |
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