Reduction of electric arc furnace dust pellets by mixture containing hydrogen

Abstract The large amount of dust generated in electric arc furnace aligned with its chemical composition makes this dust a potential source of iron in the direct reduction iron process. Thus, the aim of this research is to investigate the reduction of pellets produced with electric arc furnace dust using hydrogen as the reducing agent. The kinetic investigation was examined applying the differential method. In addition, the influence of reducing gas stream and temperature in the reduction process were investigated applying the Forced Stepwise Isothermal Analysis technique. The temperature studied varied from 500 to 1000°C with isothermals in each 50°C. The reducing gas was a mixture of 10% of hydrogen and 90% of argon. Then, the product characterization was carried out via scanning electron microscope and X-ray analysis. A thermogravimetric test showed a mass loss of 42 wt% due to the reduction of iron and zinc oxides. Besides this, the reduction occurred in three steps: 550-650°C, 700-800°C, 850-950°C. Between 550-650°C, the reduction was controlled by a nucleation mechanism with an Ea of 41.1 kJ/mol. In the second step (700-800°C), a mixed control between nucleation and diffusion was obtained with an Ea of 89.1 kJ/mol. Furthermore, a crust of iron was formed around the pellet, which hindered the reducing gas diffusion into the pellet. In the third stage (850-950°C), the formation of a sintered structure was noted, which decreased pore volume. The internal diffusion of reducing gases was determined as the controlling mechanism, with an Ea of 130.9 kJ/mol.摘要：电弧炉所产生的大量粉尘，凭借其自身的化学组成，成为直接还原铁工艺中潜在的铁源。因此，本研究旨在探究以氢气作为还原剂时，电弧炉粉尘制备球团的还原过程。本研究采用微分法开展动力学研究。此外，本研究采用强制阶梯等温分析（Forced Stepwise Isothermal Analysis）技术，探究了还原气流与温度对还原过程的影响。本次研究的温度范围设定为500至1000℃，每50℃设置一个等温点。实验所用还原气为体积占比10%氢气与90%氩气的混合气体。随后，通过扫描电子显微镜（scanning electron microscope）与X射线分析（X-ray analysis）对产物进行了表征。热重测试结果显示，因铁氧化物与锌氧化物的还原反应，试样质量损失达42 wt%。此外，还原过程可分为三个阶段：550~650℃、700~800℃以及850~950℃。在550~650℃区间，还原过程由成核机制控制，活化能（Ea）为41.1 kJ/mol。在第二阶段（700~800℃），还原过程为成核与扩散混合控制机制，活化能（Ea）为89.1 kJ/mol。此外，球团表面会形成铁壳层，阻碍还原气体向球团内部扩散。在第三阶段（850~950℃），试样会形成烧结结构，导致孔隙体积减小。此时还原气体的内部扩散为反应控制机制，活化能（Ea）为130.9 kJ/mol。