关键词: 皮江法, 硅酸钙, 真空热还原, 镁, 还原机理

Abstract: 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.

Key words: Pidgeon process, calcium silicate, vacuum-thermal reduction, magnesium, reduction mechanism