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真空碳热还原PbO-Fe2O3相变路径与挥发动力学

Phase transition pathways and volatilisation kinetics of PbO-Fe2O3 in vacuum carbon thermal reduction

  • 摘要: 电弧炉粉尘(electric arc furnace dust,EAFD)作为电弧炉炼钢过程中产生的典型危险固体废弃物,因富含铅、锌、铁等有价金属元素,具有较高的资源化利用价值。本研究以EAFD中铅的高效回收为目标,围绕PbO-Fe2O3体系的交互作用,重点考察PbO与Fe2O3的物质的量之比为1∶1的条件下真空碳热还原过程中铅还原挥发行为。通过FactSage 8.0热力学软件对体系饱和蒸气压、平衡物相组成及吉布斯自由能变化进行计算,并结合X射线衍射分析(X-ray diffraction analysis,XRD)、扫描电子显微镜-能量色散X射线光谱仪(scanning electron microscope-energy dispersive spectrometer,SEM-EDS)等表征手段,系统分析配碳量、还原温度和保温时间对物相演变、微观形貌及铅挥发率的影响。热力学结果表明,真空条件可显著降低体系反应起始温度,有利于PbO还原及金属铅挥发。铁氧化物的还原过程主要遵循Fe2O3→Fe3O4→FeO→Fe的逐级转化路径,而铅主要经历PbO(s)→Pb(l)→Pb(g)的还原挥发过程。试验结果表明,当还原温度为1 150 ℃、配碳量(碳质量分数)为16%、保温时间为60 min时,体系中铅的挥发效果最佳,铅挥发率可达到99%以上,实现了铅与铁相的高效分离。动力学分析进一步表明,PbO真空碳热还原过程可分为不同控制阶段。反应前期主要受界面化学反应控制,表观活化能由123.60 kJ/mol升高至152.17 kJ/mol;反应后期逐渐转变为气体扩散控制,表观活化能稳定在150.33~155.49 kJ/mol。研究结果阐明了PbO-Fe2O3体系在真空碳热还原过程中的物相转化规律与铅挥发机制,可为电弧炉粉尘中铅的选择性分离与高效回收提供理论依据和工艺参考。

     

    Abstract: Electric arc furnace dust (EAFD) is typical hazardous solid waste generated during the steelmaking process in electric arc furnaces. Because it is rich in valuable metals such as lead, zinc, and iron, it holds high potential for resource utilization. This study aims for the efficient recovery of lead from EAFD. It focused on the interaction within the PbO-Fe2O3 system, specifically investigating the lead reduction and volatilization behavior during vacuum carbon thermal reduction at molar ratio of PbO and Fe2O3 was 1∶1. The FactSage 8.0 thermodynamic software was used to calculate the system's saturated vapor pressure, equilibrium phase composition, and Gibbs free energy changes. Combined with characterization methods such as X-ray diffraction analysis (XRD) and scanning electron microscope energy dispersive spectrometer (SEM-EDS), the study systematically analyzed the effects of carbon addition, reduction temperature, and holding time on phase evolution, microstructure, and the lead volatilization rate. Thermodynamic results show that vacuum conditions significantly lower the initial reaction temperature of the system, favoring the reduction of PbO and the volatilization of metallic lead. The reduction of iron oxides mainly follows the stepwise transformation path of Fe2O3→Fe3O4→FeO→Fe, while lead primarily undergoes the reduction and volatilization process of PbO(s)→Pb(l)→Pb(g). Experimental results demonstrate that under the conditions of reduction temperature of 1 150 ℃, carbon addition (mass fraction) of 16%, and holding time of 60 min, the system achieves the best lead volatilization effect, with a lead volatilization rate exceeding 99%, realizing efficient separation of lead from the iron phase. Kinetic analysis further reveals that the vacuum carbon thermal reduction process of PbO can be divided into different controlling stages. The early stage of the reaction is mainly controlled by interfacial chemical reactions, with the apparent activation energy increasing from 123.60 kJ/mol to 152.17 kJ/mol. The later stage gradually transitions to gas diffusion control, with the apparent activation energy stabilizing within the range of 150.33 to 155.49 kJ/mol. The findings elucidate the phase transformation regularities and lead volatilization mechanism in the PbO-Fe2O3 system during vacuum carbon thermal reduction, providing a theoretical basis and process reference for the selective separation and efficient recovery of lead from electric arc furnace dust.

     

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