钒钛磁铁精矿碳热还原原位铝热强化及机理

The development of the rotary hearth furnace (RHF) direct reduction process in titanomagnetite concentrates treatment is impeded by the low productivity of the RHF, due to the inability to use a multi-layer bed of composite pellets, resulting from the non-synchronous reduction of composite pellets in different layers limited by the dominant heat transfer of radiation in RHF. Therefore, the in-situ aluminothermic enhancement for carbothermic reduction of titanomagnetite concentrates was suggested in the present proposal. The enhancement and mechanism of carbothermic reduction of titanomagnetite concentrates by in-situ aluminothermic method were investigated by isothermal reduction and nonisothermal reduction combining with a series of examining methods, such as chemical analysis, X ray diffraction, mineral microscope, high temperature X ray diffraction and scanning electron microscopy. As a result, The effects of atmosphere a and temperutate on the carbothermic reduction of titanomagnetite concentrates will be known well and the mechanism of that will also be revealled. The mechanism of separation and enrichment of Fe and Ti elements and phase transiction during the reduction will be clarified. The effects of aluminum particle size and amount added on the kinetics of titanomagnetite concentrate carbothermic reduction will be found. All of the studies above will provide theory evidences for achieving to employ a multi-layer bed in RHF and the further devlopement of RHF direct reduction process of titanomagnetite concentrates.

受转底炉炉内辐射传热方式限制，不同料层含碳球团还原不同步，无法采用厚料层操作，致使转底炉生产效率低下，严重制约钒钛磁铁精矿转底炉直接还原工艺的发展。针对该问题，本项目提出钒钛磁铁精矿碳热还原原位铝热强化新方法。项目将采用等温还原和非等温还原实验方法，结合化学分析、X射线衍射、矿相显微镜、高温X射线衍射和扫描电镜等检测分析方法，对钒钛磁铁精矿碳热还原原位铝热强化及机理进行研究，认识铝热强化条件下，气氛、温度对钒钛磁铁精矿碳热过程的影响规律；探索原位铝热强化对钒钛磁铁精矿碳热还原过程中Fe、Ti元素分离富集影响机制；明确原位铝热强化钒钛磁铁精矿碳热还原过程中物相演变规律；掌握铝粉粒度和添加量对钒钛磁铁精矿碳热还原动力学的影响规律，揭示钒钛磁铁精矿碳热还原原位铝热强化作用机理，为钒钛磁铁精矿转底炉直接还原工艺实现厚料层操作和进一步发展提供理论依据。

本项目针对攀枝花钒钛磁铁精矿，采用等温还原和非等温还原等实验方法对钒钛磁铁精矿碳热还原行为、铝热强化及机理和动力学等方面展开了系统研究。为钒钛磁铁精矿转底炉直接还原工艺实现厚料层操作和进一步发展提供了理论依据。主要包括：（1）开展了铝粉粒度和添加量对钒钛磁铁精矿碳热还原过程的强化作用及机理研究。结果表明：铝粉的加入明显地加快钒钛磁铁精矿含碳球团的还原速率。铝粉粒度越细越能提高单位时间内的相对还原度，从而加速钒钛磁铁精矿的还原速率；铝粉的添加能促进还原过程中新生金属铁的形核与聚集。还原过程中，铝粉作为形核粒子促进了新生金属铁的形核；铝粉作为还原剂参与还原，放出热量，促进其周围新生金属铁的聚集长大。提出了铝热强化钒钛磁铁精矿碳热还原机理，还原温度低于960 ºC时主要还原反应为铁氧化物与煤粉直接还原反应。当还原温度超过960 ºC以后，碳的气化反应速率急剧加大，气-固还原占主导地位。前期的还原主要是铝和部分的碳参与，到了后期添加铝粉的样品还有大量的碳可以继续进行碳热还原。铝热还原反应放出的热量加快了布多尔反应的反应速率，从而加快了碳热还原的速率并提高了最终的金属化率。（2）利用非等温热分析法对钒钛磁铁精矿碳热还原过程及铝热强化还原过程进行了动力学分析，结果表明：添加铝粉样品的活化能整体上小于未添加铝粉的样品。当温度小于950 ℃之前，主要发生的是煤粉的挥发分的析出和钒钛磁铁精矿和煤粉发生的固-固反应，当温度大于超过1000 ℃时，这一阶段主要发生的是铁氧化物的还原，反应受铁氧化物还原反应控制。还原后期由于反应物被还原产物包裹，反应气体难以到达反应界面，总的反应速率受扩散控制。（3） 开展了铝热强化对钒钛磁铁精矿金属化球团熔分渣金两项分离的影响研究。结果表明：添加1%铝粉可稍微改善渣金分离；当铝粉添加量大于2%时，由于TiC的生成，渣的流动性变差，渣铁分离效果恶化。