| Hydrometallurgical process of producing manganese products demands that MnO2 in pyrolusite is reduced to acid-soluble MnO. Reduction technology of pyrolusite for producing manganese products has a great effect on the cost of production, energy consumption and operating environment. Therefore, the reduction technology of pyrolusite is an important research topic in the metallurgical industry of manganese internationally. The topic issue of reduction process is to find out a kind of reductant, which is cheap, efficient, easily to get, and less environmental pollution. A series of carbohydrates, taking glucose for instance, are bright prospect reductant and confirmed by a number of scholars. At the same time, microwave heating technology has the unique characteristics of selective heating, fast heating and uniform radiation, so it has been widely used in hydrometallurgy with significant potential advantages as a new metallurgical method.In this work, electrolytic manganese dioxide (EMD) was also taken for the research object and was leached by water-bath heating and microwave heating. The results showed that the leaching rate of manganese with water-bath heating is higher than that of microwave heating at the same temperature. The main reasons causing this phenomenon was explained by analyzing the control temperature mechanism of microwave instrument and the thermodynamics of the leaching reaction. Furthermore, through contrasting kinetics of manganese leaching with these two heating mode and calculating the apparent activation energy of leaching process, the conclusions were obtained. It is that: at low temperature, the process of leaching with water-bath heating is controlled by chemical reaction, however, with temperature increasing, the control step shifts to mixed control. But the leaching process with microwave heating is basically controlled by chemical reaction even at different temperature.The exploratory experiment of carbon powder reducing the EMD in aqueous solution was also carried out. Influence factors of the leaching rate such as the reaction temperature, reaction time, concentration of sulfuric acid and the mass ratio of C/MnO2 were investigated. The optimum conditions of reductive leaching EMD with carbon as reductant are that: reaction time is 3 h, reaction temperature is 100℃, mass ratio of C/MnO2 is 5:1, concentration of H2SO4 is 2.5 mol?L-1. The leaching rate of manganese can reach 97% under these optimum conditions. It's also found that the leaching rate of manganese increased in the presence of soluble iron. This indicated that soluble iron in the leaching process of manganese plays the role of catalyst.In this work, reductive leaching pyrolusite with glucose as reductant and in the microwave irradiation was in investigated. The optimum conditions for reductive leaching were obtained and they are as follow: the mass ratio of glucose to manganese ore is 0.5, concentration of sulfuric acid is 1 mol?L-1, the molar ratio of H2SO4/MnO2 is 2:1, reaction temperature is 80℃, the microwave power is 600 W, the reaction time is 30 min. It's found that the leaching rate of manganese under these conditions is up to 94%. The relationship between the leaching rate of manganese and the leaching time at different temperature was studied, and found that the leaching process is controlled by chemical reaction and diffusion. At low reaction temperature, the reaction rate is slow, and the leaching process was controlled by the chemical reaction. The chemical reaction rate increases rapidly with the temperature rising, and become faster than the diffusion velocity finally. As a result, leaching process is controlled by diffusion. It's also confirmed through calculating the apparent activation energy. |
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