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Experimental and Numerical Studies on a One-Step Method for the Production of Mg in the Silicothermic Reduction Process
- Zhang, Chao, Wang, Chao, Zhang, Shaojun, Guo, Liejin
- Industrial & Engineering Chemistry Research 2015 v.54 no.36 pp. 8883-8892
- activation energy, carbon dioxide, chemical reactions, dolomite, engineering, equations, furnaces, heat, industry, kinetics, magnesium, models, reaction kinetics, temperature
- In this paper, a new efficient one-step technical method was first developed for the production of magnesium in the industry. The one-step method could combine the two processes of dolomite decomposition and magnesium reduction in the magnesium reduction retort. Thus, the high-temperature carbon dioxide produced by the dolomite decomposition process could be collected in a timely manner instead of being emitted into the atmosphere, and excessive heat loss caused by the two separate processes also could be almost completely avoided. This paper presents an experimental study on the intrinsic chemical kinetics mechanisms of this new efficient one-step technology. By applying each of the most likely solid-state kinetic models, the kinetic parameters of the two reactions that reacted during the dolomite decomposition stage and magnesium reduction stage were evaluated, and the kinetic models that best verify the experimental data were attempted. For the dolomite decomposition stage of the one-step technology, the equation of the chemical kinetic model can be represented by α²/2 = kD₁τ in the temperature range of 1173–1473 K, and the apparent activation energy was determined to be 160.6 kJ mol–¹. For the magnesium reduction stage of the one-step technology, the surface reaction chemical kinetic model 1 – (1 – β)¹/³= kSτ described very satisfactorily the experimental values for the different reduction temperature. Then, a one-step model incorporating the chemical reaction kinetics of the dolomite decomposition stage and the magnesium reduction stage and heat conduction was first developed. The simulations of the impact of heating temperature on the dolomite decomposition stage and magnesium reduction stage were carried out in the reduction retorts of the furnace utilizing this model. The distribution of dolomite decomposition extent in the retorts, the total extent of dolomite decomposition with time, the distribution of magnesium reduction extent in the retorts, and the total extent of magnesium reduction with time were studied in detail. The analysis showed that the one-step technology is effective in not only reducing the cycle time of dolomite decomposition stage and magnesium reduction stage but also saving energy.