硼铁矿直接还原过程中金属铁颗粒的生长特性

 硼铁矿是中国含硼原料的主要来源,其加工利用的关键在于硼和铁的分离。研究了不同条件下硼铁矿在直接还原过程中金属铁颗粒的生长特性,可为硼铁矿中硼和铁的有效分离提供理论支撑,从而达到硼铁矿资源化利用的目的。采用Leica DMI5000M光学显微镜获得还原球团中金属铁颗粒的显微图像后,通过Image-Pro Plus 6.0图像软件对显微图像进行金属铁颗粒粒径的分析统计,并采用化学分析的方法对还原产品中铁的金属化率进行检测,同时利用扫描电镜研究了Na₂CO₃促进铁氧化物还原的作用机理和金属铁颗粒的生长行为。结果表明,Na₂CO₃作用下硼铁矿球团中的铁氧化物能有效被还原,随着还原时间的延长,还原球团中铁的金属化率和金属铁颗粒的平均粒径均有效增大,在还原温度为1 100 ℃、还原时间为60 min的条件下,不添加Na₂CO₃的焙烧产物中铁的金属化率和金属铁颗粒的平均粒径分别为84.36%和8.55 μm,而在添加15%Na₂CO₃后于同样条件下焙烧,产物中铁的金属化率和金属铁颗粒的平均粒径分别为91.72%和14.07 μm;SEM-EDS分析结果说明,Na₂CO₃不仅有促进金属铁和其他物质分离的作用,而且还会影响金属铁颗粒在还原焙烧过程中的迁移行为;在直接还原过程中,金属铁颗粒先由“点”接触变为“颈”接触,然后重新相交形成新的晶界成为多边形颗粒,最后多边形颗粒间互相连接形成致密化集合体。

Growth characteristics of metallic iron particles during direct reductive of ludwigite ore

Ludwigite ore will be the main source of boron-containing raw materials in China, and the key of its processing and utilization lies in the B-Fe separation. The growth characteristics of metallic iron particles in the direct reduction process of ludwigite ore under different conditions were investigated, which could provide theoretical support for B-Fe separation and achieve the purpose of resource utilization of ludwigite ore. The microscopic images of metallic iron particles in the reduced pellets were obtained by Leica DMI5000M optical microscope, the sizes of metallic iron particles were analyzed and counted by the software of Image-pro Plus 6.0, and then the metallization rate of iron in the reduces product was tested by chemical analysis. Meawhile, the promoting mechanism of Na₂CO₃ for iron oxide reduction and the growth behavior of metallic iron particles were studied by SEM. The results showed that the iron oxides of ludwigite ore pellets could be effectively reduced in the presence of Na₂CO₃. The metallization rate of iron and the size of metallic iron particles increased effectively with the extension of reduction time. When the pellets were roasted at 1 100 ℃ for 60 min in the absence of Na₂CO₃, the metallization rate of iron and the size of metallic iron particles in the reduced products were 84.36% and 8.55 μm. However, the metallization rate of iron and the size of metallic iron particles could reach to 91.72% and 14.07 μm with the same roasting conditions in the presence of 15% Na₂CO₃. The results of SEM-EDS analysis showed that Na₂CO₃ not only promoted the metallic iron to separate from other substances, but also affected the migration behavior of metallic iron particles during the reduction roasting process. The metallic iron particles first changed from "point" contact to "neck" contact, and then re-intersected to form new grain boundaries and became polygonal particles during the direct reducing process. Finally, the polygon particles were connected to each other to form a densified aggregate.