红土镍矿半熔融态冶炼过程金属聚集及渣金分离调控机制

Preparation of ferronickel by pyro-metallurgical smelting process from nickel laterite ore for stainless steel production is an important trend. With respect to the semi-molten smelting process, enhancing the mass transfer of ferronickel grains and adjusting the interfacial behavior between slag and metal by regulating the properties of both slag and metal phases is favorable to promote the aggregation and growth of ferronickel as well as slag-metal separation. This project is focused on the preparation of ferronickel by semi-molten smelting process. Firstly, study on the phase transformation during the smelting process is carried out, it is aimed to clear the effect of components on the high-temperature properties of slag and metal fraction. Then, in-situ confocal laser-scanning microscope (CLSM) is applied to observe the aggregation and slag-metal separation process. Various properties including the melting temperature, viscosity and surface tension are regulated to find out their effects on the aggregation and separation process. The migration behavior of metal and carbonaceous reductant as well as the distribution of the main elements in semi-molten slag will be studied systematically. The mechanism on accelerating the metal aggregation by regulating the properties of slag and metal as well as their synergy strengthening effect are revealed after that. Based on the study of high-temperature wetting behavior of slag on carbonaceous reductant and metal substrate, the effect of interfacial characteristics on metal aggregation and separation would be ascertained. Eventually, the basic theory of intensifying the aggregation and separation process by regulating the properties is expected to be established. The study of the mechanism on aggregation of ferronickel grains in the semi-molten smelting process of nickel laterite is of great significance to improve the smelting efficiency as well as reduce energy consumption and cost.

红土镍矿火法冶炼镍铁用于不锈钢生产是重要趋势。半熔融态冶炼工艺中，通过调控渣金两相高温性能来强化镍铁传质及调节渣金界面行为，能够有效促进金属聚集和渣金分离。本项目针对红土镍矿半熔融态冶炼镍铁工艺，研究冶炼过程渣金两相中各组分的演变规律，明确组分对渣金高温性能的影响；采用激光共聚焦显微镜原位观察金属聚集和分离过程，系统掌握金属相渗碳、“渗硫”，渣相熔化温度、粘度等调控方法对镍铁晶粒聚集和渣金分离的影响规律；重点研究金属和碳质还原剂在半熔融态渣相中的迁移和元素分配规律，揭示性能调控对促进镍铁晶粒聚集长大的作用机理，以及二者的协同强化机制；基于渣-碳、渣-金间界面高温润湿行为研究，探明渣-金-碳间界面特性对聚集和分离的影响；最终形成渣金性能调控强化镍铁聚集和渣金分离的基础理论。深入研究红土镍矿半熔融态冶炼过程渣金性能调控的作用机制，对提高镍铁冶炼效率、降低能耗和生产成本具有重要理论和实际意义。

镍是不锈钢的重要合金元素，红土镍矿火法冶炼镍铁用于不锈钢生产是主流趋势。本项目基于半熔融态冶炼工艺，提出通过调控渣金性能，促进冶炼过程金属聚集长大，实现金属相和渣相高效分离。通过项目研究，查明了半熔融态冶炼过程物相演变规律，明确了渣金两相的主要高温物化基础特性。镍、铁氧化物较容易被还原，钠盐可破坏硅酸盐的结构，促进镍铁元素解离，被还原后将进入金属相，钠元素将进入渣相。FeO和Na2O均有利于降低渣相的软熔温度和粘度，提高液相量；通过渗碳或“渗硫”可显著降低金属相的熔点。揭示了渣金性能调控对金属聚集和渣金分离的影响规律，建立了半熔融态冶炼工艺渣金性能调控理论基础。分别通过控制Na2S、Na2O、FeO含量调控渣相性能，控制渗碳量、“渗硫”量调控金属相性能，Na2S对金属聚集的促进效果最为显著。添加3.30%Na2S或4.47%Na2CO3可使渣金分离开始温度从1297℃分别降至1123℃、1101℃，此温度主要受渣相性能的影响。探明了渣相-金属相-碳质还原剂间高温界面行为，为渣金高效分离提供了理论依据。渣样与Ni-Fe合金基片的接触角约为60o，有利于二者的分离；渣样与石墨基片的接触角约为130o，润湿性差，不利于渣样与石墨还原剂的接触，但有利于有还原后团块与碳质耐材的分离；渣样与氧化铝基片的接触角约为30o，且渣中碱度、FeO、Al2O3含量对接触角的影响较小。基于半熔融态冶炼，开发了红土镍矿混合冶炼制备镍铁合金新工艺。褐铁矿型红土镍矿的配比从0%增加到20%时，镍铁金属颗粒的平均直径从7μm增加至45μm，镍回收率从55.17%增加至92.86%；当褐铁矿型红土镍矿配比为5%，配碳量为6.0%时，在1380℃还原30min，磁选后合金中Ni品位达到8.08%，回收率为89.26%，Fe品位为80.09%。本项目针对红土镍矿半熔融态冶炼工艺，建立了渣金性能调控的基础理论和技术原型，研究所获得的理论成果与关键技术对红土镍矿资源的高效利用具有很好的指导意义。