以硅钙合金为还原剂真空热还原炼镁的基础研究

At present，most of magnesium metal in the world is produced by Pidgeon process. Although Pidgeon process has been a great improvement in the past ten years, the magnesium production by Pidgeon process is also a kind of heavy energy and materials consumption, and heavy pollution metallurgical industry. A new method using magnesite and dolomite as materials and using Si-Ca alloy as reductant can significantly reduce the ratio of materials to magnesium and improve the utilization ratio of reductant which will reduce energy consumption and the emission of reduction slag. So the process using Si-Ca alloy as reductant is a very promising magnesium production technology. In the project, the influence mechanism of reduction conditions on the reduction ratio of MgO would be studied by a scientific research of the effect of calcination and reduction conditions on the reduction process. The reaction mechanism of reduction process by using Si-Ca alloy as reductant would be investigated according to reduction thermodynamic and kinetics analysis, heat transfer mechanism analysis and the temperature distribution simulating. The reaction behavior of fluoride addition and purities of materials and reductant in the reduction process would be studied. The basis theory system of extracting magnesium by vacuum thermal reduction using Si-Ca alloy as reductant would initially establish through this project which provides theoretical basis and technical support for improving the reduction ratio of MgO and the utilization ratio of reductant.

目前世界上的金属镁主要是用皮江法生产的，皮江法生产金属镁物料消耗大、还原料镁比高、能耗高、废渣排放量大。以白云石和菱镁石为原料，以硅钙合金为还原剂真空热还原炼镁可提高还原剂的利用率，降低还原过程料镁比，实现还原渣的循环利用，从而降低金属镁的生产能耗和废渣的排放量，是一种非常有前景的炼镁新技术。本项目通过系统研究还原条件对氧化镁还原过程的影响，借助于还原反应热力学和动力学分析，结合还原过程中物料之间的传热机制分析以及瞬态温度场模拟，阐明以硅钙合金为还原剂的真空金属热还原炼镁的还原机理和镁还原率的影响机制，同时探讨杂质和添加剂在还原过程中的反应行为及其对还原过程的影响规律，初步建立起硅钙真空热还原炼镁的基础理论体系，为进一步提高还原过程镁还原率和还原剂的利用率提供理论和技术支撑。

目前，世界上85%以上的金属镁是采用皮江法生产的。目前皮江法存在的主要问题是还原过程中的镁还原率低，从而导致原料和还原剂硅铁消耗量大以及还原过程料镁比高，导致这一问题的一个主要原因在于还原剂硅铁中部分硅以FeSi2化合物的形式存在，而硅铁化合物中硅还原氧化镁的温度较高，降低了还原反应速率和氧化镁的还原率。本项目对以白云石和菱镁石为原料，以硅钙合金为还原剂真空热还原炼镁工艺进行了研究，结合还原反应热力学和动力学分析，阐明了以硅钙合金为还原剂的真空金属热还原炼镁的还原机理，获得了杂质和氟盐添加剂在还原过程中的反应行为及其对还原过程的影响规律。研究结果表明，以硅钙合金为还原剂的炼镁过程较皮江法更容易进行，以硅钙合金为还原剂还原氧化镁的过程中，合金中钙首先参与还原反应释放出游离的单质硅，不会像硅铁合金中硅与铁生成硅铁化合物而降低硅的还原活性，从而使氧化镁的还原率较皮江法提高3%以上。此外，该方法可同炼镁还原渣的综合利用联系起来，形成炼镁还原渣碳电热还原生产硅钙合金-硅钙合金炼镁-还原渣还原生产硅钙合金的一个闭路循环，从而降低金属镁的生产能耗和废渣的排放量，是一种非常有前景的炼镁新技术。通过本项目的研究，初步建立起了硅钙真空热还原炼镁的基础理论体系，为该技术的进一步推广应用提供理论和技术支撑。