不同气氛条件下CaO-SiO2-Nb2O5-TiO2-FeO渣系的高温熔体结构和热力学性质

China has been working on the development of comprehensive utilization technology of Baiyan Obo tailings for decades, whose feature of multimetallic symbiosis leads to the complex in slag composition in smelting process of ferroniobium. The continuous enrichment of TiO2, in particular, significantly changes the melt structure of the niobium-bearing slag at high temperature and its thermodynamic properties. These facts influence not only the smelting process, but also the ferroniobium quality. However, the reported phase diagrams about the niobium-bearing slag system are mostly on the binary or ternary systems, which cannot satisfy the thermodynamic requirements of the complex metallurgical process. Thus, according to the composition of Baiyan Obo tailings, CaO-SiO2-Nb2O5-TiO2-FeO system is taken as the research slag system. Firstly, the melt structure of slag at high temperature and its thermodynamic properties will be studied under different atmosphere conditions, and the equilibrium valence state and corresponding change rule of variable valence components, such as niobium, titanium and iron, will be investigated. Secondly, activity and activity coefficient of each component will be measured and calculated, and then the iso-activity diagram, iso-thermal section and equilibrium phase diagram will be constructed. The Spatial Lever Rule will be used in the analysis of fraction of equilibrium phase in multi-component system phase diagram. Thirdly, the structure and phase transformation rule of high-temperature melt will also be studied. The work will provide a thermodynamics basis for the development of smelting process and ferroniobium quality, on the basis of which the comprehensive utilization technology of Baiyan Obo tailings will be improved.

目前，我国正致力于白云鄂博尾矿综合利用工艺的研究开发。多金属共伴生的特征造成了铌铁冶炼渣系的组成非常复杂，尤其是TiO2的不断富集严重改变了含铌渣系的高温熔体结构和热力学性质，不但给铌铁冶炼工艺带来严重困扰，而且影响铌铁合金的品质。现有的含铌渣系相图多为简单的二元或三元体系，无法满足复杂冶金过程的热力学需求。项目根据白云鄂博尾矿的成分特征，选择CaO-SiO2-Nb2O5-TiO2-FeO渣系为对象，系统研究不同气氛条件下熔渣的高温熔体结构和热力学性质，确定铌、钛、铁等变价组元的平衡价态及其变化规律，测定并计算各渣系组元的活度和活度系数，绘制典型成分区间的等活度图、等温截面图和平衡相图，利用空间杠杆定律探索分析多元冶金相图中的固相平衡比例关系，精确解析熔渣的高温熔体结构与相变规律。研究工作将为铌铁冶炼工艺的开发和铌铁合金品质的提升提供热力学依据，推动白云鄂博尾矿综合利用工艺的发展。

以白云鄂博为原矿的铌铁冶炼渣的渣系复杂，尤其是TiO2的不断富集严重改变了含铌渣系的高温熔体结构和热力学性质，不但给铌铁冶炼工艺带来严重困扰，而且影响铌铁合金的品质。现有的含铌渣系相图多为简单的二元或三元体系，无法满足复杂冶金过程的热力学需求。本项目根据白云鄂博尾矿的成分特征，选择CaO-SiO2-Nb2O5-TiO2-FeO渣系为对象，系统研究不同气氛条件下熔渣的高温熔体结构和相应的热力学性质，最终确定在CaO-SiO2-Nb2O5-TiO2-FexOy五元渣系中Nb2O5、TiO2、Fe2O3组元在熔渣中作为网络中间体，分别以四面体和八面体的结构共存。SiO2根据桥氧数目的不同分别以Q0、Q1、Q2、Q3四种四面体形式存在。并绘制出CaO-SiO2-Nb2O5-TiO2-FeO五元渣系在1400~1600 ℃温度条件下含铌组元的等活度图和相关相图，得到铌铁冶炼过程中，高温、低w(CaO)/w(SiO2)以及w(Nb2O5)的增加有利于直接合金化提铌。确定了不同气氛条件下渣系的相变过程和固相共存关系，以及温度和气氛对固相共存关系的影响作用。1200℃和1300℃空气气氛条件下分别确定了8种和4种相平衡关系，以及还原性气氛条件下2件相平衡关系。利用杠杆定律对多元空间相图进行了分析应用，结合高温平衡实验结果和子体系相图信息，利用插值和函数拟合计算绘制出了CaO-SiO2-Nb2O5-TiO2-FeO五元渣的等温截面图和空间相图。研究结果可以直接应用于铌铁冶炼和相关含铌渣系的研究与开发工作，为铌铁合金品质的提升和相关工艺的设计提供了热力学依据，并对白云鄂博尾矿综合利用工艺的发展具有重要的实用价值。