皮江法炼镁还原机理

用XRD和SEM?EDS对不同还原温度下所得皮江法炼镁还原渣的主要物相与分布规律进行分析，分析了镁、硅与钙的扩散过程，探讨了皮江法炼镁的还原机理。结果表明，以硅铁合金为还原剂的还原炼镁过程是简单的固?固反应，Si还原MgO的起始温度为900~950℃，还原反应主要在高于1050℃时进行，温度低于1000℃时MgO还原率很低。还原反应首先在CaO?MgO颗粒与Si颗粒的交界面进行，反应生成的镁蒸汽从反应区域逸出并在结晶区结晶，未反应的Si向外扩散穿过反应区域继续还原MgO。还原过程中，以单质存在的Si全部参与反应，与CaO结合生成Ca2SiO4, FeSi2在还原反应过程中部分分解为FeSi和Si，而FeSi, FeSi2及Fe2Si3(FeSi与FeSi2的混合物)中的Si还原MgO的温度较高，较难参与还原反应，造成Si损失，是硅铁还原MgO还原率较低的主要原因。

Reduction mechanism of Pidgeon process of magnesium metal

Pidgeon process using dolomite as materials and using ferrosilicon as reductant is the main method of magnesium metal production, and the low reduction rate of MgO is one of the main problems for this method. Some experiments of Pidgeon process were carried out in this work. The phase compositions of reductant and ferrosilicon alloy were analyzed. XRD and SEM?EDS were used to study the phases and the distribution of phases in reduction slag obtained at different reduction temperatures. The reduction mechanism of Pidgeon process was explored by studying the diffusion process of silicon, magnesium and calcium element. The reason for low reduction rate of MgO was investigated by studying the existent form of ferrosilicon in reduction slag and conversion of ferrosilicon in reduction process. The results showed that the reduction process of Pidgeon was a simple solid?solid reaction process, and the initial reduction temperature of MgO by silicon was about 900?950℃. The reduction rate of MgO was very low when the reduction temperature was lower than 1000℃, and the reduction rate was accelerated when the reduction temperature was over 1050℃. The reaction was carried out at the interface of CaO?MgO particles and silicon particle, and the MgO was reduced to magnesium vapor which escapes from the reaction layer and condenses on crystallizer, then silicon diffuse outwards crossed the reaction layer and continued to reduce MgO. In reduction process, all the silicon in the form of simple substance took part in the reduction reaction of MgO and reacted with CaO to form Ca2SiO4, but only part of FeSi2 decomposed to FeSi and Si. The reduction temperature of FeSi and Fe2Si3 which obtained by the reaction of FeSi with FeSi2 was higher and they were difficult to reduce MgO at industrial reduction temperature, so they remained in the reduction slag which lead to lower utilization of silicon and low reduction rate of MgO in Pidgeon process.