Catalytic Research On Carbothermic Reduction Of Magnesia

With global resources and environmental protection become more and moreserious, the application fields of magnesium and it’s alloys extend continually at homeand abroad which are honoured as the most potential "green engineering materials", andthe demand for magnesium increase substantially. This greatly promotes the progress intechnology for magnesium manufacturing. At present,the technology mainly compriseelectrolytic route and silicothermic process, and both have some problems such as highcost, big energy consumption and serious pollution. Researchers at home and abroaduse cheap carbon as reducing agent, utilize the vacuum metallurgy, and form a methodfor carbothermic reduction of magnesia in vacuum, and the cost of raw material reducesgreatly. But by now, for carbothermic reduction in vacuum, the reduction temperature ishigh, reduction ratio of magnesia is low, and reversible reaction control difficultly.Therefore, seeking a method of low temperature and high reduction ratio is the key ofcarbothermic reduction for magnesium. This work is mainly adding fluoride forcatalytic reduction to reduce the reduction temperature, and increase magnesiumreduction ratio, achieving the purpose of high efficiency and low energy consumption.The experiments of carbothermic reduction of magnesia are carried throughchoosing graphite as reducing agent, obtain a result of low weightlessness of the sample,and conclude that the reducibility of graphite is poor. So several kinds of commoncarbonaceous reducing agents are used for comparison experiment, and the reducingagent suitable for carbothermic reduction is selected. the reduction reaction in differentconditions is taken place by adding different types and contents of fluoride as catalyst.The content of magnesia left in the reduced slag is measured with the atomic absorptionspectrometry, and the reduction ratio of magnesia is obtained. The catalytic effect oftypes and contents of fluoride for carbothermic reduction of magnesia is discussed. Theexperimental results show that:（1） With graphite as reducing agent, reduction experiments in different parameterscondition are carried out. In the optimum conditions, weightlessness of pellet is lower,only27%or so.（2） Comparing of reduction ratioes of magnesia with several commoncarbonaceous reducing agents, the reducibility is as follows: coke> charcoal> activatedcharcoal> graphite, and coke is the best reductant. （3） The orthogonal experiment with coke as reducing agent shows that, in thisexperimental conditions, factor influence of carbothermic reduction of magnesia is: theparticle size of coke was most important, followed by soaking time, carbon content andleast-important temperature. The optimum process is time for120min, temperature for1600℃, carbon ratiofor1:3and carbon particle size for-240mesh.（4） Adding fluoride can obviously increases the reaction rate of reduction. Withincrease of fluoride content, the reduction rate of magnesia improves greatly. At lowerreduction temperature and time, the reduction effect of MgF₂is better than CaF₂.Raising temperature and extensing time, the catalytic effect of CaF₂is superior thanMgF₂.（5） With calcined dolomite as raw material, catalytic effect of fluoride forcarbonathemic reduction is verified. The results show that reduction ratio of calcineddolomite can amount to more than80%by adding5%fluoride at1400℃for30min,and the catalytic effect of CaF₂is better than MgF₂.