Reduction Kinetics and Microscopic Properties Transformation of Boron-Bearing Iron Concentrate–Carbon-Mixed Pellets

ABSTRACT

Selective reduction followed by magnetic or melting separation is an innovative and effective method for the comprehensive utilization of boron-bearing iron concentrate. As the raw material of boron products, the reserve of szaibelyite ore is significantly depleted. Therefore, the comprehensive utilization of boron-bearing iron ore resources becomes more and more important. To study the reduction kinetics in depth, a boron-bearing iron concentrate containing 52.18% total iron and 5.50% B₂O₃ was reduced isothermally with coke as the reductant. The results showed that both the reduction degree and the maximum reduction rate increased with temperature and C/O molar ratio (fixed carbon in the coke to oxygen in iron oxides in the ore). 98.00% reduction degree and 0.00414 s⁻¹ maximum reduction rate were achieved at 1523K of reduction temperature and 1.4 of C/O molar ratio. The reduction kinetics can be best described by Avrami–Erofeev model, g(α) = [−ln(1-α)]^3/2. The apparent activation energy and pre-exponential factor were 264.565 kJ·mol⁻¹ and 1.87 × 10⁷ s⁻¹, respectively. The phase transformation observed by XRD agreed well with the results of reduction degree analysis. The micro-structure evolution behavior of the pellets was analyzed by SEM and EDS. As the reduction time increased from 0 to 600 s, most of the iron oxides were reduced to metallic iron, leaving other major elements in the slag phase. The slag phase mainly consisted of the solid solution of Mg₂SiO₄ and Mg₃B₂O₆. With further increase to 1200 s, the metallic iron particles migrated and flocculated together forming bigger particles.

摘要

选择性还原-磁选（熔分）新技术是实现含硼铁精矿综合利用的有效方法。由于生产硼产品的原料硼镁石大量消耗，使得含硼铁精矿中硼、铁资源的综合利用越发重要。本研究以焦炭为还原剂，对某铁品位 52.18%、含硼 5.50% 的含硼铁精矿进行了系统的等温还原动力学研究。结果显示，还原度和最大还原速率随还原温度和 C/O 摩尔比的增加而增加，并在还原温度 1523K 、 C/O 摩尔比 1.4 的条件下分别达到 98.00% 和 0.00414 s⁻¹。含硼铁精矿的选择性还原过程符合Avrami-Erofeev模型，g(α)= [-ln(1-α)]^3/2，相应的表观活化能和指前因子分别为 264.565 kJ·mol⁻¹ 和 1.87×10⁷ s⁻¹。采用XRD测试技术考察了含硼铁精矿还原过程的物相变化，其结果与还原度变化规律展现出较好的一致性。借助SEM-EDS 分析，研究了含硼铁精矿球团微观结构演变规律，发现还原时间延长至 600s 时，绝大部分铁氧化物被还原为金属铁；还原时间为 1200s 时，金属铁颗粒实现了聚集长大。硼元素主要分布在由 Mg₂SiO₄ 和 Mg₃B₂O₆ 固溶体组成的渣相中。

KEYWORDS:

• Boron-bearing iron concentrate
• reduction kinetics
• phase transformation
• microstructure

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (51674065, 51204033).