红土镍矿固态还原中硫化物微区熔体的界面作用机制

It is of great significance for the healthy and sustainable development of the stainless steel industry, to produce ferronickel from laterite as the feedstock instead of electrolytic nickel for stainless steel manufacture. In the laterite nickel ore solid state reduction-magnetic separation process, a suitable amount of liquid can significantly promote the mass transfer and ferronickel grain growth, aggregation, whereas the interfacial structure and properties of the microzone melt determine the basic behavior of ferronickel grain growth. This project adopting the diffusion couple, single/double wire thermocouple (SHTT/DHTT) and drop method etc. focus on investigating the phase transformation of laterite during solid-state reduction in the presence of sulfide additives, the wettability between sulfide melt with ferronickel and olivine as well as the melting and crystallization behaviors of sulfide melt. After revealing the mechanisms of interfacial structure, properties, composition and content of sulfide melt on the solute migration, distribution, and ferronickel grain nucleation and growth behavior, we can correlate relationships between raw material performance, process parameters and melt properties, composition and content with ferronickel grain growth. Eventually, grain growth regulation theories based on the interfacial interaction mechanism of microzone sulfide melt. This project has important theoretical significance for the further understanding of mechanism of microzone melt in the solid state reduction and provides important ideas and solutions to the new technologies by virtue of solid-state reduction for the preparation of ferronickel from laterite.

以红土镍矿为原料生产镍铁替代电解镍冶炼不锈钢，对支撑不锈钢工业的健康可持续发展意义重大。红土镍矿固态还原-磁选制备镍铁工艺中，适量液相的存在可显著促进传质过程和镍铁晶粒生长、聚集，而微区熔体的界面结构及性质决定了镍铁晶粒生长的基本行为。本项目运用扩散偶、单/双丝热电偶（SHTT/DHTT）、座滴法等手段，重点研究含硫添加剂作用下红土镍矿固态还原过程中各组分的转化规律、硫化物熔体对镍铁、橄榄石质基底的高温润湿性及其熔化、结晶性能，揭示硫化物熔体界面结构、性质、成分和含量对溶质迁移、分配与镍铁晶粒形核、生长行为的作用机制，建立原料性能、工艺参数、熔体性质、成分及含量与镍铁晶粒生长之间的匹配关系，最终构建基于硫化物微区熔体界面作用机制的镍铁晶粒生长调控理论基础。项目研究结果对进一步认识微区熔体的界面作用机制具有重要的理论意义，可为基于红土镍矿固态还原的镍铁制备新工艺的发展提供重要思路和解决方案。

本项目重点研究含硫添加剂作用下红土镍矿固态还原过程中各组分的转化规律、硫化物熔体对镍铁、橄榄石质基底的高温润湿性及其熔化、结晶性能，揭示硫化物熔体界面结构、性质、成分和含量对溶质迁移、分配与镍铁晶粒形核、生长行为的作用机制。查明了红土镍矿的选择性还原/硫化特性，确定了镍、铁氧化物选择性还原/硫化的动力学机制，硫酸钠作用下可实现镍、铁氧化物选择性硫化，红土镍矿还原焙烧过程中，铁氧化物的还原反应受界面化学反应控制，镍氧化物的还原受一级化学反应控制，镍氧化物还原反应的速率常数均远高于铁氧化物的还原反应速率常数。建立了红土镍矿还原物相转变、熔融特性温度与镍铁晶粒生长之间的匹配关系，阐明了基于液相烧结理论的硫酸钠促进镍铁晶粒生长作用机制。添加硫酸钠可显著降低体系的软熔特性温度，Fe-FeS低共熔点化合物的形成是降低红土镍矿—硫酸钠还原体系软熔特性温度的主要原因，液相的形成加速了红土镍矿—硫酸钠还原体系的传质过程，促进了镍铁晶粒的生长、聚集。对于镍铁晶粒的生长而言，升高还原温度和延长还原均有利于其粒径的增长。项目研究结果对进一步认识微区熔体的界面作用机制具有重要的理论意义，可为基于红土镍矿固态还原的镍铁制备新工艺的发展提供重要思路和解决方案，并可扩展应用于复杂铁矿（硼镁铁矿、高铝铁矿、鲕状赤铁矿等）综合利用新技术的开发。